/* ==========================================================================
   Studyloom — design system
   ========================================================================== */

:root {
  color-scheme: light;
  --bg: #f6f4ef;
  --bg-elev: #ffffff;
  --bg-sunken: #efece5;
  --bg-hover: rgba(27, 31, 42, 0.045);
  --ink: #1b1f2a;
  --ink-2: #444b5b;
  --ink-3: #6c7383;
  --ink-4: #9a9fab;
  --line: #e4e0d6;
  --line-strong: #d2ccbe;
  --accent: #3446d4;
  --accent-hover: #2a3abb;
  --accent-ink: #ffffff;
  --accent-soft: #e9ebfc;
  --accent-text: #2c3bb8;
  --like: #d6336c;
  --like-soft: #fce9f0;
  --success: #17804f;
  --success-soft: #e2f3e9;
  --success-line: #b5dfc6;
  --warn: #9a5800;
  --warn-soft: #fdf2dd;
  --danger: #c0262d;
  --danger-soft: #fdeaea;
  --mark: #ffe9a0;
  --on-success: #ffffff;
  --mark-ink: #3b2f00;
  --code-bg: #f1eee7;
  --shadow-sm: 0 1px 2px rgba(23, 25, 35, 0.06);
  --shadow: 0 1px 2px rgba(23, 25, 35, 0.05), 0 6px 20px rgba(23, 25, 35, 0.06);
  --shadow-lg: 0 18px 50px rgba(23, 25, 35, 0.16), 0 2px 6px rgba(23, 25, 35, 0.06);
  --ring: 0 0 0 3px rgba(52, 70, 212, 0.28);

  --sub-l-ink: 36%;
  --sub-s-ink: 58%;
  --sub-l-bg: 95%;
  --sub-s-bg: 70%;
  --sub-l-line: 84%;
  --sub-l-solid: 46%;

  --radius-xs: 4px;
  --radius-sm: 7px;
  --radius: 11px;
  --radius-lg: 16px;
  --radius-xl: 22px;

  --font-sans: ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-serif: "Iowan Old Style", "Palatino Linotype", Palatino, "Book Antiqua", "URW Palladio L", Georgia, serif;
  --font-mono: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;

  --header-h: 64px;
  --container: 1200px;
  --gutter: 24px;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    color-scheme: dark;
    --bg: #101319;
    --bg-elev: #171b23;
    --bg-sunken: #0c0f14;
    --bg-hover: rgba(255, 255, 255, 0.05);
    --ink: #e8eaf0;
    --ink-2: #bcc2ce;
    --ink-3: #8d94a3;
    --ink-4: #646b79;
    --line: #262b36;
    --line-strong: #353b48;
    --accent: #7b8cff;
    --accent-hover: #93a1ff;
    --accent-ink: #0d1020;
    --accent-soft: #1f2443;
    --accent-text: #a3afff;
    --like: #ff6b9a;
    --like-soft: #3a1826;
    --success: #4cc68a;
    --success-soft: #12291e;
    --success-line: #1f4a35;
    --warn: #f0b45a;
    --warn-soft: #2c2210;
    --danger: #ff7a7a;
    --danger-soft: #331517;
    --mark: #5a4a0e;
    --on-success: #08170f;
    --mark-ink: #fff3c4;
    --code-bg: #11151c;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 8px 24px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 18px 50px rgba(0, 0, 0, 0.55);
    --ring: 0 0 0 3px rgba(123, 140, 255, 0.35);
    --sub-l-ink: 76%;
    --sub-s-ink: 75%;
    --sub-l-bg: 16%;
    --sub-s-bg: 32%;
    --sub-l-line: 28%;
    --sub-l-solid: 62%;
  }
}

:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #101319;
  --bg-elev: #171b23;
  --bg-sunken: #0c0f14;
  --bg-hover: rgba(255, 255, 255, 0.05);
  --ink: #e8eaf0;
  --ink-2: #bcc2ce;
  --ink-3: #8d94a3;
  --ink-4: #646b79;
  --line: #262b36;
  --line-strong: #353b48;
  --accent: #7b8cff;
  --accent-hover: #93a1ff;
  --accent-ink: #0d1020;
  --accent-soft: #1f2443;
  --accent-text: #a3afff;
  --like: #ff6b9a;
  --like-soft: #3a1826;
  --success: #4cc68a;
  --success-soft: #12291e;
  --success-line: #1f4a35;
  --warn: #f0b45a;
  --warn-soft: #2c2210;
  --danger: #ff7a7a;
  --danger-soft: #331517;
  --mark: #5a4a0e;
  --on-success: #08170f;
  --mark-ink: #fff3c4;
  --code-bg: #11151c;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 8px 24px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 18px 50px rgba(0, 0, 0, 0.55);
  --ring: 0 0 0 3px rgba(123, 140, 255, 0.35);
  --sub-l-ink: 76%;
  --sub-s-ink: 75%;
  --sub-l-bg: 16%;
  --sub-s-bg: 32%;
  --sub-l-line: 28%;
  --sub-l-solid: 62%;
}

/* Elements carrying a subject hue (style="--h: 228") get derived colors. */
.hue {
  --h: 228;
  --sub-ink: hsl(var(--h) var(--sub-s-ink) var(--sub-l-ink));
  --sub-bg: hsl(var(--h) var(--sub-s-bg) var(--sub-l-bg));
  --sub-line: hsl(var(--h) 40% var(--sub-l-line));
  --sub-solid: hsl(var(--h) 62% var(--sub-l-solid));
}

/* ------------------------------------------------------------------ base */

*, *::before, *::after { box-sizing: border-box; }
/* Components set display on their own classes, which would otherwise beat the hidden attribute. */
[hidden] { display: none !important; }

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-padding-top: calc(var(--header-h) + 16px);
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 400 16px/1.6 var(--font-sans);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  overflow-x: hidden;
}

a { color: var(--accent-text); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 2px; }
img, svg { display: block; max-width: 100%; }
button, input, select, textarea { font: inherit; color: inherit; }
button { cursor: pointer; }
:focus-visible { outline: none; box-shadow: var(--ring); border-radius: var(--radius-xs); }
::selection { background: color-mix(in srgb, var(--accent) 22%, transparent); }

h1, h2, h3, h4 { margin: 0; line-height: 1.25; font-weight: 600; letter-spacing: -0.01em; }
.serif { font-family: var(--font-serif); }
p { margin: 0 0 0.9em; }

.skip-link {
  position: absolute; left: 12px; top: -48px; z-index: 100;
  background: var(--accent); color: var(--accent-ink); padding: 8px 14px; border-radius: var(--radius-sm);
}
.skip-link:focus { top: 12px; }

.sr-only {
  position: absolute !important; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0;
}

.container { width: 100%; max-width: var(--container); margin: 0 auto; padding: 0 var(--gutter); }

main { flex: 1; outline: none; }
.page { padding-top: 28px; padding-bottom: 72px; }
.page-narrow { max-width: 780px; }

/* ------------------------------------------------------------------ header */

.site-header {
  position: sticky; top: 0; z-index: 40;
  height: var(--header-h);
  background: color-mix(in srgb, var(--bg) 86%, transparent);
  backdrop-filter: saturate(1.4) blur(14px);
  -webkit-backdrop-filter: saturate(1.4) blur(14px);
  border-bottom: 1px solid var(--line);
}
.header-inner { height: 100%; display: flex; align-items: center; gap: 20px; }

.brand { display: flex; align-items: center; gap: 10px; color: var(--ink); flex-shrink: 0; }
.brand:hover { text-decoration: none; }
.brand-mark {
  width: 34px; height: 34px; border-radius: 9px;
  display: grid; place-items: center;
  background: var(--ink); color: var(--bg);
  font: 600 20px/1 var(--font-serif);
  position: relative;
}
.brand-mark::after {
  content: ""; position: absolute; right: 5px; top: 5px; width: 5px; height: 5px; border-radius: 50%;
  background: var(--accent);
}
.brand-name { font: 600 21px/1 var(--font-serif); letter-spacing: -0.01em; }

.main-nav { display: flex; align-items: center; gap: 2px; }
.main-nav a {
  padding: 7px 11px; border-radius: var(--radius-sm); color: var(--ink-2); font-size: 14.5px; font-weight: 500;
}
.main-nav a:hover { background: var(--bg-hover); color: var(--ink); text-decoration: none; }
.main-nav a[aria-current="page"] { color: var(--ink); background: var(--bg-hover); }

/* Secondary sections and the theme switch sit under "More", leaving the bar's width to search.
   On phones the same links are listed inline in the menu drawer. */
.nav-more-btn {
  display: flex; align-items: center; gap: 3px; padding: 7px 8px 7px 11px; border: 0; border-radius: var(--radius-sm);
  background: none; color: var(--ink-2); font-size: 14.5px; font-weight: 500;
}
.nav-more-btn svg { width: 15px; height: 15px; transition: transform 0.15s; }
.nav-more-btn:hover, .nav-more.open .nav-more-btn, .nav-more:has([aria-current="page"]) .nav-more-btn { background: var(--bg-hover); color: var(--ink); }
.nav-more.open .nav-more-btn svg { transform: rotate(180deg); }
.nav-more .menu-pop { left: 0; right: auto; min-width: 200px; }
.nav-more .menu-pop a, .nav-more .theme-item { color: var(--ink-2); }
.nav-more .menu-pop a[aria-current="page"] { color: var(--ink); background: var(--bg-hover); }
.nav-more .theme-item { position: relative; margin-top: 7px; }
.nav-more .theme-item::before { content: ""; position: absolute; left: -6px; right: -6px; top: -4px; border-top: 1px solid var(--line); }

.header-search { flex: 1; min-width: 140px; max-width: 560px; margin-left: auto; }
@media (min-width: 761px) and (max-width: 1000px) {
  .header-inner { gap: 12px; }
  .brand-name, .header-actions .signup-btn, .header-actions .ask-btn span, .user-btn .rep { display: none; }
  .header-actions .ask-btn { width: 38px; padding: 0; }
}
@media (max-width: 1100px) { .header-search .kbd { display: none; } }
.header-actions { display: flex; align-items: center; gap: 6px; flex-shrink: 0; }
.login-btn svg { display: none; }
.icon-btn.menu-toggle { display: none; }

/* ------------------------------------------------------------------ buttons */

.btn {
  --btn-bg: var(--bg-elev); --btn-ink: var(--ink); --btn-line: var(--line-strong);
  display: inline-flex; align-items: center; justify-content: center; gap: 7px;
  height: 38px; padding: 0 15px; border-radius: var(--radius-sm);
  border: 1px solid var(--btn-line); background: var(--btn-bg); color: var(--btn-ink);
  font-size: 14.5px; font-weight: 550; white-space: nowrap; line-height: 1;
  transition: background .15s, border-color .15s, box-shadow .15s, transform .05s;
}
.btn:hover { text-decoration: none; background: color-mix(in srgb, var(--btn-bg) 92%, var(--ink)); }
.btn:active { transform: translateY(1px); }
.btn:disabled, .btn[aria-disabled="true"] { opacity: .55; cursor: not-allowed; transform: none; }
.btn svg { width: 17px; height: 17px; flex-shrink: 0; }
.btn-primary { --btn-bg: var(--accent); --btn-ink: var(--accent-ink); --btn-line: transparent; box-shadow: var(--shadow-sm); }
.btn-primary:hover { background: var(--accent-hover); }
.btn-ghost { --btn-bg: transparent; --btn-line: transparent; color: var(--ink-2); }
.btn-ghost:hover { background: var(--bg-hover); color: var(--ink); }
.btn-danger { --btn-ink: var(--danger); }
.btn-danger.btn-solid { --btn-bg: var(--danger); --btn-ink: #fff; --btn-line: transparent; }
.btn-sm { height: 32px; padding: 0 11px; font-size: 13.5px; }
.btn-xs { height: 28px; padding: 0 9px; font-size: 13px; gap: 5px; }
.btn-xs svg { width: 15px; height: 15px; }
.btn-lg { height: 46px; padding: 0 22px; font-size: 16px; border-radius: var(--radius); }
.btn-icon { width: 38px; padding: 0; }
.btn-icon.btn-sm { width: 32px; }
.btn-block { width: 100%; }
.btn.loading { position: relative; color: transparent !important; pointer-events: none; }
.btn.loading::after {
  content: ""; position: absolute; width: 16px; height: 16px; border-radius: 50%;
  border: 2px solid var(--btn-ink); border-right-color: transparent; animation: spin .7s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

.icon-btn {
  position: relative; width: 38px; height: 38px; display: grid; place-items: center;
  border-radius: var(--radius-sm); border: 0; background: transparent; color: var(--ink-2);
}
.icon-btn:hover { background: var(--bg-hover); color: var(--ink); }
.icon-btn svg { width: 20px; height: 20px; }
.icon-btn .dot {
  position: absolute; top: 5px; right: 4px; min-width: 17px; height: 17px; padding: 0 4px;
  border-radius: 9px; background: var(--like); color: #fff; font-size: 10.5px; font-weight: 700;
  display: grid; place-items: center; border: 2px solid var(--bg);
}

/* ------------------------------------------------------------------ forms */

.field { display: grid; gap: 6px; margin-bottom: 18px; }
.field > label, .label { font-size: 14px; font-weight: 600; color: var(--ink); }
.field .hint { font-size: 13px; color: var(--ink-3); }
.field .error-text { font-size: 13px; color: var(--danger); }
.input, .select, .textarea {
  width: 100%; height: 42px; padding: 0 13px;
  border: 1px solid var(--line-strong); border-radius: var(--radius-sm);
  background: var(--bg-elev); color: var(--ink); font-size: 15px;
  transition: border-color .15s, box-shadow .15s;
}
.textarea { height: auto; padding: 11px 13px; line-height: 1.55; resize: vertical; }
.input::placeholder, .textarea::placeholder { color: var(--ink-4); }
.input:focus, .select:focus, .textarea:focus { outline: none; border-color: var(--accent); box-shadow: var(--ring); }
.input[aria-invalid="true"], .textarea[aria-invalid="true"] { border-color: var(--danger); }
.select {
  appearance: none; padding-right: 36px; cursor: pointer;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%23888' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");
  background-repeat: no-repeat; background-position: right 11px center; background-size: 16px;
}
.checkbox { display: flex; gap: 10px; align-items: flex-start; font-size: 14px; color: var(--ink-2); cursor: pointer; }
.checkbox input { width: 17px; height: 17px; margin: 2px 0 0; accent-color: var(--accent); flex-shrink: 0; }

.segmented {
  display: inline-flex; padding: 3px; gap: 2px; border-radius: var(--radius-sm);
  background: var(--bg-sunken); border: 1px solid var(--line);
}
.segmented button, .segmented a {
  border: 0; background: transparent; color: var(--ink-3); padding: 6px 12px; border-radius: 5px;
  font-size: 13.5px; font-weight: 550; white-space: nowrap;
}
.segmented button:hover, .segmented a:hover { color: var(--ink); text-decoration: none; }
.segmented [aria-pressed="true"], .segmented [aria-current="true"] {
  background: var(--bg-elev); color: var(--ink); box-shadow: var(--shadow-sm);
}

.tabs { display: flex; gap: 4px; border-bottom: 1px solid var(--line); margin-bottom: 4px; overflow-x: auto; scrollbar-width: none; }
.tabs::-webkit-scrollbar { display: none; }
.tabs a, .tabs button {
  padding: 10px 12px; border: 0; background: none; color: var(--ink-3); font-size: 14.5px; font-weight: 550;
  border-bottom: 2px solid transparent; margin-bottom: -1px; white-space: nowrap;
}
.tabs a:hover, .tabs button:hover { color: var(--ink); text-decoration: none; }
.tabs [aria-current="true"] { color: var(--ink); border-bottom-color: var(--ink); }
.tabs .count { color: var(--ink-4); font-weight: 500; margin-left: 4px; }

/* ------------------------------------------------------------------ cards & primitives */

.card {
  background: var(--bg-elev); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
}
.card-pad { padding: 20px; }
.card-title { font-size: 13px; font-weight: 650; text-transform: uppercase; letter-spacing: .06em; color: var(--ink-3); margin-bottom: 12px; }
.section-title { font: 600 23px/1.2 var(--font-serif); letter-spacing: -0.01em; }
.section-head { display: flex; align-items: baseline; justify-content: space-between; gap: 16px; margin-bottom: 14px; }
.section-head a { font-size: 14px; }
.muted { color: var(--ink-3); }
.small { font-size: 13.5px; }
.nowrap { white-space: nowrap; }
.row { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.stack > * + * { margin-top: 16px; }
.spacer { flex: 1; }
.divider { height: 1px; background: var(--line); border: 0; margin: 20px 0; }

.chip {
  display: inline-flex; align-items: center; gap: 6px; height: 26px; padding: 0 9px 0 4px;
  border-radius: 13px; background: var(--sub-bg); color: var(--sub-ink); border: 1px solid var(--sub-line);
  font-size: 12.5px; font-weight: 600; white-space: nowrap; max-width: 100%;
}
.chip:hover { text-decoration: none; filter: brightness(0.97); }
.chip-sym {
  width: 19px; height: 19px; border-radius: 6px; display: grid; place-items: center;
  background: var(--sub-solid); color: #fff; font: 600 10.5px/1 var(--font-serif);
}
.chip.plain { padding: 0 9px; }
.topic-link { font-size: 13px; color: var(--ink-2); font-weight: 500; }

.tag {
  display: inline-flex; align-items: center; height: 24px; padding: 0 8px; border-radius: var(--radius-xs);
  background: var(--bg-sunken); color: var(--ink-2); font-size: 12.5px; font-family: var(--font-mono); border: 1px solid var(--line);
}
.tag:hover { text-decoration: none; color: var(--ink); border-color: var(--line-strong); }

.badge {
  display: inline-flex; align-items: center; gap: 4px; height: 22px; padding: 0 8px; border-radius: 11px;
  font-size: 12px; font-weight: 650; letter-spacing: .01em; white-space: nowrap;
  background: var(--bg-sunken); color: var(--ink-2); border: 1px solid var(--line);
}
.badge svg { width: 13px; height: 13px; }
.badge-problem { background: var(--warn-soft); color: var(--warn); border-color: transparent; }
.badge-success { background: var(--success-soft); color: var(--success); border-color: transparent; }
.badge-accent { background: var(--accent-soft); color: var(--accent-text); border-color: transparent; }
.diff { display: inline-flex; align-items: center; gap: 5px; font-size: 12.5px; color: var(--ink-3); font-weight: 550; }
.diff i { width: 5px; height: 11px; border-radius: 2px; background: var(--line-strong); display: inline-block; }
.diff i.on { background: var(--ink-2); }

.avatar {
  --size: 32px;
  width: var(--size); height: var(--size); border-radius: 50%; flex-shrink: 0;
  display: grid; place-items: center; color: #fff; font-weight: 650;
  font-size: calc(var(--size) * 0.4); letter-spacing: -.02em; user-select: none;
  background: linear-gradient(140deg, hsl(var(--h) 60% 55%), hsl(calc(var(--h) + 40) 55% 42%));
}

.kbd {
  font: 500 11.5px/1 var(--font-mono); padding: 3px 5px; border-radius: 4px; color: var(--ink-3);
  border: 1px solid var(--line-strong); background: var(--bg-elev); box-shadow: 0 1px 0 var(--line-strong);
}

.empty {
  text-align: center; padding: 48px 20px; color: var(--ink-3);
  border: 1px dashed var(--line-strong); border-radius: var(--radius); background: color-mix(in srgb, var(--bg-elev) 50%, transparent);
}
.empty h3 { color: var(--ink); font: 600 20px/1.3 var(--font-serif); margin-bottom: 6px; }
.empty p { max-width: 460px; margin: 0 auto 16px; }

.notice {
  display: flex; gap: 10px; align-items: flex-start; padding: 12px 14px; border-radius: var(--radius-sm);
  background: var(--accent-soft); color: var(--accent-text); font-size: 14px; margin-bottom: 16px;
}
.notice svg { width: 18px; height: 18px; flex-shrink: 0; margin-top: 2px; }
.notice.warn { background: var(--warn-soft); color: var(--warn); }
.notice.danger { background: var(--danger-soft); color: var(--danger); }
.notice a { color: inherit; font-weight: 650; text-decoration: underline; }

.skeleton {
  border-radius: 6px; height: 14px; margin: 9px 0;
  background: linear-gradient(90deg, var(--bg-sunken) 25%, color-mix(in srgb, var(--bg-sunken) 40%, var(--bg-elev)) 50%, var(--bg-sunken) 75%);
  background-size: 200% 100%; animation: shimmer 1.3s infinite;
}
@keyframes shimmer { to { background-position: -200% 0; } }

.progress {
  position: fixed; top: 0; left: 0; height: 2px; width: 0; z-index: 60; background: var(--accent);
  transition: width .25s ease, opacity .3s; opacity: 0; pointer-events: none;
}
.progress.active { opacity: 1; }

/* ------------------------------------------------------------------ layout grids */

.layout { display: grid; grid-template-columns: minmax(0, 1fr) 300px; gap: 36px; align-items: start; }
.layout-left { display: grid; grid-template-columns: 236px minmax(0, 1fr); gap: 32px; align-items: start; }
.aside { display: grid; gap: 18px; position: sticky; top: calc(var(--header-h) + 20px); }
.breadcrumb { display: flex; align-items: center; flex-wrap: wrap; gap: 6px; font-size: 13.5px; color: var(--ink-3); margin-bottom: 14px; }
.breadcrumb a { color: var(--ink-3); }
.breadcrumb a:hover { color: var(--ink); }
.breadcrumb svg { width: 14px; height: 14px; opacity: .6; }

.page-head { margin-bottom: 24px; }
.page-title { font: 600 34px/1.15 var(--font-serif); letter-spacing: -0.02em; }
.page-sub { color: var(--ink-3); margin-top: 8px; font-size: 16px; max-width: 680px; }

/* ------------------------------------------------------------------ home */

.hero {
  position: relative; padding: 56px 0 44px; overflow: hidden;
  border-bottom: 1px solid var(--line);
  background:
    radial-gradient(900px 400px at 85% -10%, color-mix(in srgb, var(--accent) 10%, transparent), transparent 70%),
    radial-gradient(600px 300px at -5% 110%, color-mix(in srgb, #e08a2e 9%, transparent), transparent 70%);
}
.hero-grid { display: grid; grid-template-columns: minmax(0, 1.15fr) minmax(0, 0.85fr); gap: 56px; align-items: center; }
.eyebrow {
  display: inline-flex; align-items: center; gap: 8px; font-size: 13px; font-weight: 650; color: var(--ink-2);
  padding: 5px 11px 5px 6px; border-radius: 20px; background: var(--bg-elev); border: 1px solid var(--line); box-shadow: var(--shadow-sm);
}
.eyebrow b { background: var(--accent); color: var(--accent-ink); padding: 2px 7px; border-radius: 10px; font-size: 11.5px; }
.hero h1 { font: 600 clamp(40px, 6vw, 64px)/1.03 var(--font-serif); letter-spacing: -0.03em; margin: 18px 0 16px; }
.hero h1 em { font-style: italic; color: var(--accent-text); }
.hero-lede { font-size: 18px; color: var(--ink-2); max-width: 560px; margin-bottom: 26px; }
.hero-search { max-width: 600px; }
.popular { display: flex; flex-wrap: wrap; align-items: center; gap: 7px; margin-top: 16px; font-size: 13.5px; color: var(--ink-3); }
.popular a {
  padding: 4px 11px; border-radius: 14px; background: var(--bg-elev); border: 1px solid var(--line); color: var(--ink-2); font-size: 13px;
}
.popular a:hover { border-color: var(--line-strong); color: var(--ink); text-decoration: none; }

.formula-stack { position: relative; height: 300px; }
.formula-card {
  position: absolute; inset: 0; margin: auto; height: 210px; width: 100%;
  display: flex; flex-direction: column; justify-content: space-between; padding: 22px 24px;
  background: var(--bg-elev); border: 1px solid var(--line); border-radius: var(--radius-lg); box-shadow: var(--shadow-lg);
  transition: transform .7s cubic-bezier(.2, .8, .2, 1), opacity .7s;
}
.formula-card .fc-head { display: flex; align-items: center; justify-content: space-between; }
.formula-card .fc-math { font-size: 21px; text-align: center; overflow: hidden; color: var(--ink); }
.formula-card .fc-math .katex-display { margin: 0; overflow: hidden; padding: 0; }
.formula-card .fc-caption { font-size: 13.5px; color: var(--ink-3); }
.formula-card[data-pos="0"] { transform: translateY(0) rotate(-1.2deg); opacity: 1; z-index: 3; }
.formula-card[data-pos="1"] { transform: translate(18px, -22px) rotate(2deg) scale(.96); opacity: .7; z-index: 2; }
.formula-card[data-pos="2"] { transform: translate(34px, -42px) rotate(4.5deg) scale(.92); opacity: .4; z-index: 1; }
.formula-card[data-pos="out"] { transform: translate(-40px, 30px) rotate(-6deg) scale(.98); opacity: 0; z-index: 4; }
.formula-card[data-pos="hidden"] { opacity: 0; transform: translate(40px, -60px) rotate(6deg) scale(.9); z-index: 0; }

.stats-strip {
  display: grid; grid-template-columns: repeat(4, 1fr); margin-top: 40px;
  border: 1px solid var(--line); border-radius: var(--radius); background: var(--bg-elev); overflow: hidden;
}
.stats-strip > div { padding: 16px 20px; border-left: 1px solid var(--line); }
.stats-strip > div:first-child { border-left: 0; }
.stat-num { font: 600 28px/1.1 var(--font-serif); letter-spacing: -0.02em; }
.stat-label { font-size: 13px; color: var(--ink-3); margin-top: 2px; }

/* Periodic table of subjects: category groups flow side by side like element blocks. */
.ptable-wrap { display: flex; flex-wrap: wrap; gap: 26px 30px; }
.ptable-group { flex: 0 0 auto; min-width: 0; }
.ptable-label { font-size: 12px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; color: var(--ink-3); margin-bottom: 10px; display: flex; align-items: center; gap: 10px; }
.ptable-label::after { content: ""; flex: 1; height: 1px; background: var(--line); }
.ptable { display: grid; grid-auto-flow: column; grid-auto-columns: 112px; gap: 8px; }
.subjects-page .ptable-wrap { margin-bottom: 8px; }
.tile {
  position: relative; display: flex; flex-direction: column; justify-content: space-between;
  aspect-ratio: 1 / 1.02; padding: 10px 12px 11px; border-radius: var(--radius);
  background: var(--sub-bg); border: 1px solid var(--sub-line); color: var(--sub-ink);
  transition: transform .18s cubic-bezier(.2, .8, .2, 1), box-shadow .18s, border-color .18s;
}
.tile:hover { text-decoration: none; transform: translateY(-3px); box-shadow: var(--shadow); border-color: var(--sub-solid); }
.tile-top { display: flex; justify-content: space-between; font: 600 11.5px/1 var(--font-mono); opacity: .8; }
.tile-sym { font: 600 36px/1 var(--font-serif); letter-spacing: -0.02em; color: var(--sub-ink); }
.tile-name { font-size: 13px; font-weight: 650; line-height: 1.25; color: var(--ink); }
.tile-count { font-size: 11.5px; color: var(--ink-3); margin-top: 2px; }

.home-cols { display: grid; grid-template-columns: minmax(0, 1fr) 340px; gap: 40px; margin-top: 52px; align-items: start; }
.how-steps { display: grid; gap: 14px; counter-reset: step; }
.how-steps li { list-style: none; display: grid; grid-template-columns: 28px 1fr; gap: 12px; font-size: 14px; color: var(--ink-2); }
.how-steps li::before {
  counter-increment: step; content: counter(step); width: 26px; height: 26px; border-radius: 50%;
  display: grid; place-items: center; background: var(--accent-soft); color: var(--accent-text); font-weight: 700; font-size: 13px;
}
.how-steps b { display: block; color: var(--ink); font-size: 14.5px; }
.how-steps { padding: 0; margin: 0; }

/* ------------------------------------------------------------------ question list */

.q-list { display: flex; flex-direction: column; }
.q-item {
  display: grid; grid-template-columns: 84px minmax(0, 1fr); gap: 18px; padding: 18px 4px;
  border-bottom: 1px solid var(--line);
}
.q-item:first-child { border-top: 1px solid var(--line); }
.q-list.flush .q-item:first-child { border-top: 0; }
.q-stats { display: flex; flex-direction: column; align-items: flex-end; gap: 6px; font-size: 13px; color: var(--ink-3); padding-top: 2px; }
.q-stat { display: flex; align-items: center; gap: 5px; white-space: nowrap; }
.q-stat b { color: var(--ink-2); font-weight: 650; }
.q-stat.answers { padding: 2px 7px; border-radius: 6px; border: 1px solid var(--line-strong); }
.q-stat.answers.has { border-color: var(--success-line); color: var(--success); }
.q-stat.answers.has b { color: var(--success); }
.q-stat.answers.accepted { background: var(--success); border-color: var(--success); color: var(--on-success); }
.q-stat.answers.accepted b { color: var(--on-success); }
.q-stat svg { width: 14px; height: 14px; }
.q-title { font-size: 17px; font-weight: 600; line-height: 1.38; color: var(--ink); display: inline; }
.q-title:hover { color: var(--accent-text); text-decoration: none; }
.q-title .katex { font-size: 1.04em; }
.q-excerpt { font-size: 14.5px; color: var(--ink-2); margin: 6px 0 10px; line-height: 1.55; overflow-wrap: anywhere; }
.q-excerpt .katex { font-size: 1em; }
.q-meta { display: flex; align-items: center; flex-wrap: wrap; gap: 8px; font-size: 13px; color: var(--ink-3); }
.q-meta .by { display: inline-flex; align-items: center; gap: 6px; margin-left: auto; }
.q-meta .by .avatar { --size: 20px; font-size: 9px; }
.q-meta .by a { color: var(--ink-2); font-weight: 550; }
.q-item.compact { grid-template-columns: minmax(0, 1fr); padding: 14px 2px; gap: 6px; }
.q-item.compact .q-title { font-size: 15.5px; }
.q-item.compact .q-meta .by { margin-left: 0; }

mark { background: var(--mark); color: var(--mark-ink); border-radius: 3px; padding: 0 1px; }

/* ------------------------------------------------------------------ question page */

.q-head { margin-bottom: 22px; }
.q-head h1 { font: 600 clamp(26px, 3.4vw, 34px)/1.2 var(--font-serif); letter-spacing: -0.02em; overflow-wrap: anywhere; }
.q-head h1 .katex { font-size: 0.98em; }
.q-head .q-meta { margin-top: 12px; gap: 14px; }
.q-head .q-meta span b { color: var(--ink-2); font-weight: 600; }

.post { display: grid; grid-template-columns: minmax(0, 1fr); gap: 0; }
.post + .post { margin-top: 0; }
.answer {
  padding: 24px 0; border-top: 1px solid var(--line);
}
.answer.accepted { position: relative; }
.accepted-banner {
  display: inline-flex; align-items: center; gap: 6px; font-size: 13px; font-weight: 650; color: var(--success);
  background: var(--success-soft); padding: 4px 10px 4px 7px; border-radius: 14px; margin-bottom: 14px;
}
.accepted-banner svg { width: 15px; height: 15px; }

.post-footer { display: flex; align-items: flex-end; justify-content: space-between; gap: 16px; margin-top: 18px; flex-wrap: wrap; }
.post-actions { display: flex; align-items: center; gap: 2px; flex-wrap: wrap; margin-left: -8px; }
.post-actions .btn { color: var(--ink-3); }
.post-actions .btn:hover { color: var(--ink); }
.author-card {
  display: flex; align-items: center; gap: 10px; padding: 9px 12px; border-radius: var(--radius-sm);
  background: var(--bg-sunken); font-size: 13px; min-width: 200px;
}
.author-card.op { background: var(--accent-soft); }
.author-card .avatar { --size: 34px; }
.author-card .who a { font-weight: 650; color: var(--ink); font-size: 14px; }
.author-card .meta { color: var(--ink-3); font-size: 12.5px; }
.rep { color: var(--ink-3); font-weight: 600; font-size: 12.5px; }

.like-btn {
  display: inline-flex; align-items: center; gap: 6px; height: 32px; padding: 0 11px; border-radius: 16px;
  border: 1px solid var(--line-strong); background: var(--bg-elev); color: var(--ink-2); font-size: 13.5px; font-weight: 600;
  transition: background .15s, color .15s, border-color .15s;
}
.like-btn svg { width: 16px; height: 16px; transition: transform .25s cubic-bezier(.3, 1.6, .5, 1); }
.like-btn:hover { border-color: var(--like); color: var(--like); }
.like-btn[aria-pressed="true"] { background: var(--like-soft); border-color: transparent; color: var(--like); }
.like-btn[aria-pressed="true"] svg { fill: currentColor; transform: scale(1.12); }
.like-btn.pop svg { animation: pop .4s cubic-bezier(.3, 1.6, .5, 1); }
@keyframes pop { 40% { transform: scale(1.4); } }
.like-btn.sm { height: 26px; padding: 0 8px; border: 0; background: transparent; font-size: 12.5px; gap: 4px; }
.like-btn.sm svg { width: 14px; height: 14px; }
.like-btn.sm[aria-pressed="true"] { background: var(--like-soft); }

.answers-head { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin: 36px 0 0; padding-bottom: 14px; }
.answers-head h2 { font: 600 22px/1.2 var(--font-serif); }
.your-answer { margin-top: 36px; padding-top: 28px; border-top: 1px solid var(--line); }
.your-answer h2 { font: 600 22px/1.2 var(--font-serif); margin-bottom: 14px; }

/* Rendered texmd/1 content */
.prose { font-size: 16.5px; line-height: 1.72; color: var(--ink); overflow-wrap: break-word; }
.prose > :first-child { margin-top: 0; }
.prose > :last-child { margin-bottom: 0; }
.prose p { margin: 0 0 1em; }
.prose h3, .prose h4, .prose h5 { font-family: var(--font-serif); margin: 1.4em 0 .5em; }
.prose h3 { font-size: 1.32em; }
.prose h4 { font-size: 1.15em; }
.prose h5 { font-size: 1em; }
.prose ul, .prose ol { padding-left: 1.5em; margin: 0 0 1em; }
.prose li { margin: .3em 0; }
.prose li > p { margin: 0 0 .4em; }
.prose blockquote {
  margin: 0 0 1em; padding: 4px 0 4px 16px; border-left: 3px solid var(--line-strong); color: var(--ink-2);
}
.prose blockquote p:last-child { margin-bottom: 0; }
.prose hr { border: 0; height: 1px; background: var(--line); margin: 1.6em 0; }
.prose code {
  font: 0.86em/1.4 var(--font-mono); background: var(--code-bg); border: 1px solid var(--line);
  padding: 1px 5px; border-radius: 5px; overflow-wrap: anywhere;
}
.prose pre.code-block {
  position: relative; margin: 0 0 1.1em; padding: 14px 16px; overflow-x: auto;
  background: var(--code-bg); border: 1px solid var(--line); border-radius: var(--radius-sm); line-height: 1.55;
}
.prose pre.code-block code { border: 0; padding: 0; background: none; font-size: 13.5px; overflow-wrap: normal; white-space: pre; }
.prose pre.code-block[data-lang]::before {
  content: attr(data-lang); position: absolute; top: 6px; right: 10px; font: 600 10.5px/1 var(--font-mono);
  text-transform: uppercase; letter-spacing: .06em; color: var(--ink-4);
}
.prose .table-wrap { overflow-x: auto; margin: 0 0 1.1em; border: 1px solid var(--line); border-radius: var(--radius-sm); }
.prose table { border-collapse: collapse; width: 100%; font-size: .94em; }
.prose th, .prose td { padding: 8px 12px; border-bottom: 1px solid var(--line); text-align: left; }
.prose th { background: var(--bg-sunken); font-weight: 650; }
.prose tr:last-child td { border-bottom: 0; }
.prose .math-block { margin: 0 0 1em; }
.prose a { text-decoration: underline; text-decoration-color: color-mix(in srgb, currentColor 35%, transparent); text-underline-offset: 2px; }
.prose del { color: var(--ink-3); }
.katex { font-size: 1.08em; }
.katex-display { margin: .9em 0; overflow-x: auto; overflow-y: hidden; padding: 4px 2px; }
.katex-display > .katex { white-space: nowrap; }
.katex-error { color: var(--danger) !important; background: var(--danger-soft); border-radius: 3px; padding: 0 3px; font-family: var(--font-mono); font-size: .88em; }
.tex-src { color: var(--ink-3); }

.prose.compact { font-size: 15px; line-height: 1.62; }
.prose.compact p { margin-bottom: .6em; }
.prose.compact .katex-display { margin: .5em 0; }

/* ------------------------------------------------------------------ comment threads */

.thread { margin-top: 18px; }
.thread-list { display: flex; flex-direction: column; }
.comment { position: relative; }
.comment-row { display: grid; grid-template-columns: 26px minmax(0, 1fr); gap: 10px; padding: 9px 0 4px; }
.comment-row .avatar { --size: 26px; font-size: 10.5px; margin-top: 2px; }
.comment-head { display: flex; align-items: center; flex-wrap: wrap; gap: 6px; font-size: 13px; color: var(--ink-3); line-height: 1.3; }
.comment-head a.name { font-weight: 650; color: var(--ink); }
.comment-head .op-tag { font-size: 11px; font-weight: 700; padding: 1px 6px; border-radius: 8px; background: var(--accent-soft); color: var(--accent-text); }
.comment-body { margin-top: 3px; }
.comment-body.deleted { color: var(--ink-4); font-style: italic; font-size: 14px; }
.comment-actions { display: flex; align-items: center; gap: 2px; margin: 2px 0 0 -6px; }
.comment-actions .btn { height: 26px; padding: 0 7px; font-size: 12.5px; color: var(--ink-3); }
.comment-actions .btn:hover { color: var(--ink); }
.comment-children { margin-left: 12px; padding-left: 23px; border-left: 2px solid var(--line); }
.comment-children:empty { display: none; }
.comment.collapsed > .comment-children, .comment.collapsed > .comment-row .comment-body, .comment.collapsed > .comment-row .comment-actions { display: none; }
.collapse-btn {
  border: 0; background: none; padding: 0 2px; color: var(--ink-4); font: 600 12px/1 var(--font-mono);
}
.collapse-btn:hover { color: var(--ink); }
.thread-footer { margin-top: 6px; }
.add-comment-btn { color: var(--ink-3); font-size: 13.5px; border: 0; background: none; padding: 6px 0; font-weight: 550; display: inline-flex; gap: 6px; align-items: center; }
.add-comment-btn:hover { color: var(--accent-text); }
.add-comment-btn svg { width: 15px; height: 15px; }
.composer { margin: 8px 0 10px; }
.flash { animation: flash 2s ease-out; border-radius: var(--radius-sm); }
@keyframes flash { 0%, 30% { background: color-mix(in srgb, var(--accent) 12%, transparent); } 100% { background: transparent; } }

/* ------------------------------------------------------------------ editor */

.editor {
  border: 1px solid var(--line-strong); border-radius: var(--radius); background: var(--bg-elev);
  transition: border-color .15s, box-shadow .15s; overflow: hidden;
}
.editor:focus-within { border-color: var(--accent); box-shadow: var(--ring); }
.editor.invalid { border-color: var(--danger); }
.editor-toolbar {
  display: flex; align-items: center; gap: 2px; padding: 5px 6px; border-bottom: 1px solid var(--line);
  background: var(--bg-sunken); flex-wrap: wrap;
}
.tb-group { display: flex; gap: 1px; padding: 0 4px; border-right: 1px solid var(--line); }
.tb-group:last-of-type { border-right: 0; }
.tb-btn {
  min-width: 30px; height: 30px; padding: 0 6px; border: 0; border-radius: 5px; background: transparent;
  color: var(--ink-2); font-size: 13.5px; display: grid; place-items: center; line-height: 1;
}
.tb-btn:hover { background: var(--bg-elev); color: var(--ink); box-shadow: var(--shadow-sm); }
.tb-btn svg { width: 16px; height: 16px; }
.tb-btn .katex { font-size: 1em; pointer-events: none; }
.tb-btn.text { font-weight: 600; font-family: var(--font-serif); font-size: 15px; }
.tb-menu { position: relative; }
.tb-pop {
  position: absolute; top: 34px; left: 0; z-index: 20; display: none; grid-template-columns: repeat(8, 34px); gap: 2px;
  padding: 8px; background: var(--bg-elev); border: 1px solid var(--line); border-radius: var(--radius-sm); box-shadow: var(--shadow-lg);
}
.tb-pop.open { display: grid; }
.tb-pop .tb-btn { width: 34px; height: 34px; }
.editor-views { margin-left: auto; padding-left: 6px; }
.editor-views .segmented { padding: 2px; }
.editor-views .segmented button { padding: 4px 9px; font-size: 12.5px; }
.editor-panes { display: grid; grid-template-columns: minmax(0, 1fr); }
.editor[data-view="split"] .editor-panes { grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); }
.editor[data-view="write"] .editor-preview { display: none; }
.editor[data-view="preview"] .editor-input { display: none; }
.editor-input {
  display: block; width: 100%; border: 0; resize: vertical; padding: 14px 16px; background: transparent; color: var(--ink);
  font: 14.5px/1.65 var(--font-mono); min-height: 220px; tab-size: 4;
}
.editor-input:focus { outline: none; }
.editor-preview { padding: 14px 18px; min-height: 220px; max-height: 640px; overflow: auto; border-left: 1px solid var(--line); background: var(--bg); }
.editor[data-view="preview"] .editor-preview { border-left: 0; }
.editor-preview .placeholder { color: var(--ink-4); font-style: italic; }
.editor-status {
  display: flex; align-items: center; gap: 12px; padding: 7px 12px; border-top: 1px solid var(--line);
  font-size: 12.5px; color: var(--ink-3); background: var(--bg-sunken); flex-wrap: wrap;
}
.editor-status .ok { color: var(--success); display: inline-flex; align-items: center; gap: 5px; }
.editor-status .ok svg, .editor-status .err svg { width: 14px; height: 14px; }
.editor-status .err { color: var(--danger); display: inline-flex; align-items: center; gap: 5px; }
.editor-status .count { margin-left: auto; font-family: var(--font-mono); }
.editor-issues { padding: 0 12px 8px; background: var(--bg-sunken); font-size: 12.5px; display: grid; gap: 4px; }
.editor-issues:empty { display: none; }
.editor-issue { display: flex; gap: 8px; align-items: baseline; text-align: left; border: 0; background: none; padding: 2px 0; color: var(--danger); }
.editor-issue.warn { color: var(--warn); }
.editor-issue code { font-family: var(--font-mono); background: var(--bg-elev); padding: 0 4px; border-radius: 3px; color: var(--ink-2); }
.editor-issue .ln { font-family: var(--font-mono); color: var(--ink-3); white-space: nowrap; }
.editor.compact .editor-input { min-height: 72px; font-size: 14px; padding: 10px 12px; }
.editor.compact .editor-preview { min-height: 72px; padding: 10px 14px; }
.editor-actions { display: flex; align-items: center; justify-content: flex-end; gap: 8px; margin-top: 10px; }
.editor-actions .hint { margin-right: auto; font-size: 12.5px; color: var(--ink-3); }

/* ------------------------------------------------------------------ search */

.search-box { position: relative; }
.search-field {
  display: flex; align-items: center; gap: 8px; height: 40px; padding: 0 6px 0 12px;
  background: var(--bg-elev); border: 1px solid var(--line-strong); border-radius: var(--radius-sm);
  transition: border-color .15s, box-shadow .15s;
}
.search-field:focus-within { border-color: var(--accent); box-shadow: var(--ring); }
.search-field > svg { width: 18px; height: 18px; color: var(--ink-3); flex-shrink: 0; }
.search-field input { flex: 1; min-width: 0; border: 0; background: transparent; outline: none; font-size: 15px; height: 100%; }
.search-field input::placeholder { color: var(--ink-4); }
.search-field input::-webkit-search-cancel-button { display: none; }
.search-box.large .search-field { height: 56px; border-radius: var(--radius); padding: 0 8px 0 18px; box-shadow: var(--shadow); }
.search-box.large .search-field input { font-size: 17px; }
.search-box.large .search-field > svg { width: 21px; height: 21px; }
.search-dropdown {
  position: absolute; top: calc(100% + 6px); left: 0; right: 0; z-index: 50;
  background: var(--bg-elev); border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow-lg);
  padding: 6px; max-height: min(70vh, 520px); overflow-y: auto; display: none;
}
.search-dropdown.open { display: block; }
.sd-section { font-size: 11.5px; font-weight: 700; letter-spacing: .07em; text-transform: uppercase; color: var(--ink-4); padding: 8px 10px 4px; }
.sd-item {
  display: flex; align-items: center; gap: 10px; padding: 8px 10px; border-radius: var(--radius-sm); color: var(--ink); cursor: pointer;
}
.sd-item:hover, .sd-item[aria-selected="true"] { background: var(--bg-hover); text-decoration: none; }
.sd-item .sd-icon { width: 26px; height: 26px; border-radius: 7px; display: grid; place-items: center; flex-shrink: 0; background: var(--bg-sunken); color: var(--ink-3); }
.sd-item .sd-icon svg { width: 15px; height: 15px; }
.sd-item .sd-icon.sym { background: var(--sub-solid); color: #fff; font: 600 12px/1 var(--font-serif); }
.sd-item .sd-text { min-width: 0; flex: 1; }
.sd-item .sd-label { font-size: 14.5px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.sd-item .sd-label .katex { font-size: 1em; }
.sd-item .sd-sub { font-size: 12.5px; color: var(--ink-3); }
.sd-footer { display: flex; justify-content: space-between; gap: 10px; padding: 8px 10px 4px; border-top: 1px solid var(--line); margin-top: 4px; font-size: 12px; color: var(--ink-3); }
.sd-footer .kbd { margin: 0 2px; }

.search-meta { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; margin: 18px 0 8px; }
.search-meta .count { color: var(--ink-3); font-size: 14px; }
.search-meta .count b { color: var(--ink); }
.parsed-filters { display: flex; gap: 6px; flex-wrap: wrap; margin-top: 10px; }
.filter-pill {
  display: inline-flex; align-items: center; gap: 6px; height: 28px; padding: 0 6px 0 10px; border-radius: 14px;
  background: var(--accent-soft); color: var(--accent-text); font-size: 13px; font-weight: 600; border: 0;
}
.filter-pill svg { width: 14px; height: 14px; }
.filter-pill:hover { filter: brightness(.96); text-decoration: none; }

.facets { display: grid; gap: 22px; position: sticky; top: calc(var(--header-h) + 20px); }
.facet h4 { font-size: 12px; font-weight: 700; text-transform: uppercase; letter-spacing: .07em; color: var(--ink-3); margin-bottom: 8px; }
.facet-list { display: grid; gap: 1px; }
.facet-item {
  display: flex; align-items: center; gap: 8px; padding: 6px 8px; border-radius: var(--radius-sm); color: var(--ink-2); font-size: 14px;
}
.facet-item:hover { background: var(--bg-hover); text-decoration: none; color: var(--ink); }
.facet-item[aria-current="true"] { background: var(--accent-soft); color: var(--accent-text); font-weight: 600; }
.facet-item .n { margin-left: auto; font-size: 12.5px; color: var(--ink-4); font-variant-numeric: tabular-nums; }
.facet-item.zero { opacity: .45; }
.facet-swatch { width: 10px; height: 10px; border-radius: 3px; background: var(--sub-solid); flex-shrink: 0; }

.result { padding: 18px 2px; border-bottom: 1px solid var(--line); }
.result .q-title { font-size: 18px; }
.result-snippet { font-size: 14.5px; color: var(--ink-2); margin: 7px 0 9px; line-height: 1.6; overflow-wrap: anywhere; }
.result-snippet .katex { font-size: 1em; }
.match-note { display: flex; align-items: center; gap: 5px; font-size: 12.5px; color: var(--ink-3); margin-bottom: 4px; }
.match-note svg { width: 13px; height: 13px; }
.topic-results { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 10px; margin: 12px 0 4px; }
.topic-card {
  display: grid; grid-template-columns: 40px 1fr; gap: 12px; align-items: center; padding: 12px; border-radius: var(--radius);
  background: var(--bg-elev); border: 1px solid var(--line); color: var(--ink);
}
.topic-card:hover { text-decoration: none; border-color: var(--sub-solid); }
.topic-card .sym { width: 40px; height: 40px; border-radius: 10px; display: grid; place-items: center; background: var(--sub-bg); color: var(--sub-ink); font: 600 18px/1 var(--font-serif); border: 1px solid var(--sub-line); }
.topic-card .name { font-weight: 650; font-size: 14.5px; line-height: 1.3; }
.topic-card .sub { font-size: 12.5px; color: var(--ink-3); }

.pagination { display: flex; gap: 4px; justify-content: center; margin-top: 28px; flex-wrap: wrap; }
.pagination a, .pagination span {
  min-width: 36px; height: 36px; padding: 0 10px; border-radius: var(--radius-sm); display: grid; place-items: center;
  border: 1px solid var(--line); color: var(--ink-2); font-size: 14px; background: var(--bg-elev);
}
.pagination a:hover { border-color: var(--line-strong); text-decoration: none; color: var(--ink); }
.pagination [aria-current="page"] { background: var(--ink); color: var(--bg); border-color: var(--ink); }
.pagination span.gap { border: 0; background: none; }

.operators { font-size: 13px; color: var(--ink-3); margin-top: 10px; line-height: 1.9; }
.operators code { font: 12.5px var(--font-mono); background: var(--bg-elev); border: 1px solid var(--line); padding: 1px 6px; border-radius: 4px; color: var(--ink-2); }

/* ------------------------------------------------------------------ subject & topic pages */

.subject-hero {
  display: grid; grid-template-columns: 112px minmax(0, 1fr) auto; gap: 26px; align-items: center;
  padding: 26px; border-radius: var(--radius-lg); background: var(--sub-bg); border: 1px solid var(--sub-line); margin-bottom: 30px;
}
.subject-hero .big-tile {
  width: 112px; height: 112px; border-radius: 18px; background: var(--bg-elev); border: 1px solid var(--sub-line);
  display: flex; flex-direction: column; justify-content: space-between; padding: 10px 12px; color: var(--sub-ink); box-shadow: var(--shadow-sm);
}
.big-tile .n { font: 600 12px/1 var(--font-mono); opacity: .8; }
.big-tile .s { font: 600 48px/1 var(--font-serif); letter-spacing: -0.03em; }
.subject-hero h1 { font: 600 36px/1.1 var(--font-serif); letter-spacing: -0.02em; color: var(--ink); }
.subject-hero p { color: var(--ink-2); margin: 8px 0 0; max-width: 640px; }
.subject-hero .meta { display: flex; gap: 18px; margin-top: 12px; font-size: 14px; color: var(--ink-2); }
.subject-hero .meta b { font-weight: 700; color: var(--ink); }
.topic-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 10px; margin-bottom: 36px; }
.topic-tile {
  display: flex; flex-direction: column; gap: 4px; padding: 14px 15px; border-radius: var(--radius);
  background: var(--bg-elev); border: 1px solid var(--line); color: var(--ink); transition: border-color .15s, transform .15s;
}
.topic-tile:hover { text-decoration: none; border-color: var(--sub-solid); transform: translateY(-1px); }
.topic-tile .name { font-weight: 650; font-size: 15px; }
.topic-tile .desc { font-size: 13px; color: var(--ink-3); line-height: 1.45; flex: 1; }
.topic-tile .counts { font-size: 12.5px; color: var(--ink-3); margin-top: 6px; display: flex; gap: 10px; }
.topic-tile .counts b { color: var(--ink-2); }
.sibling-topics { display: flex; gap: 6px; flex-wrap: wrap; margin-top: 14px; }
.sibling-topics a { font-size: 13px; padding: 4px 10px; border-radius: 14px; border: 1px solid var(--line); color: var(--ink-2); background: var(--bg-elev); }
.sibling-topics a:hover { border-color: var(--sub-solid); text-decoration: none; color: var(--ink); }
.sibling-topics a[aria-current="page"] { background: var(--sub-solid); border-color: var(--sub-solid); color: #fff; }

.contributor { display: flex; align-items: center; gap: 10px; padding: 7px 0; font-size: 14px; }
.contributor .avatar { --size: 30px; }
.contributor a { color: var(--ink); font-weight: 600; }
.contributor .small { color: var(--ink-3); }

.subjects-index { display: grid; gap: 34px; }
.subject-row { display: grid; grid-template-columns: 260px minmax(0, 1fr); gap: 24px; padding: 22px 0; border-top: 1px solid var(--line); }
.subject-row .head { display: flex; gap: 14px; align-items: flex-start; }
.subject-row .head .mini-tile {
  width: 52px; height: 52px; border-radius: 12px; display: grid; place-items: center; flex-shrink: 0;
  background: var(--sub-bg); border: 1px solid var(--sub-line); color: var(--sub-ink); font: 600 23px/1 var(--font-serif);
}
.subject-row .head a { color: var(--ink); font-weight: 650; font-size: 17px; }
.subject-row .head p { font-size: 13.5px; color: var(--ink-3); margin: 4px 0 0; }
.subject-row .topics { display: flex; flex-wrap: wrap; gap: 7px; align-content: flex-start; }
.subject-row .topics a {
  font-size: 13.5px; padding: 5px 11px; border-radius: 16px; background: var(--bg-elev); border: 1px solid var(--line); color: var(--ink-2);
}
.subject-row .topics a:hover { border-color: var(--sub-solid); color: var(--ink); text-decoration: none; }
.subject-row .topics a .n { color: var(--ink-4); margin-left: 5px; font-size: 12px; }

/* ------------------------------------------------------------------ ask page */

.ask-grid { display: grid; grid-template-columns: minmax(0, 1fr) 300px; gap: 36px; align-items: start; }
.similar-box { margin-top: 10px; border: 1px solid var(--line); border-radius: var(--radius-sm); background: var(--bg-elev); display: none; }
.similar-box.open { display: block; }
.similar-box .head { padding: 9px 12px; font-size: 13px; font-weight: 650; color: var(--ink-2); border-bottom: 1px solid var(--line); display: flex; gap: 6px; align-items: center; }
.similar-box .head svg { width: 15px; height: 15px; color: var(--warn); }
.similar-box a { display: flex; gap: 10px; align-items: center; padding: 8px 12px; font-size: 14px; color: var(--ink); border-bottom: 1px solid var(--line); }
.similar-box a:last-child { border-bottom: 0; }
.similar-box a:hover { background: var(--bg-hover); text-decoration: none; }
.similar-box a .n { margin-left: auto; font-size: 12px; color: var(--ink-3); white-space: nowrap; }
.similar-box a .n.acc { color: var(--success); font-weight: 650; }
.form-row { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.tag-input {
  display: flex; flex-wrap: wrap; gap: 6px; align-items: center; min-height: 42px; padding: 5px 8px;
  border: 1px solid var(--line-strong); border-radius: var(--radius-sm); background: var(--bg-elev);
}
.tag-input:focus-within { border-color: var(--accent); box-shadow: var(--ring); }
.tag-input input { flex: 1; min-width: 120px; border: 0; outline: none; background: transparent; height: 30px; font-size: 14.5px; }
.tag-input .tag button { border: 0; background: none; padding: 0 0 0 4px; color: var(--ink-3); font-size: 14px; line-height: 1; }
.tips { font-size: 14px; color: var(--ink-2); }
.tips ol, .tips ul { padding-left: 18px; margin: 0; display: grid; gap: 8px; }
.cheat { display: grid; grid-template-columns: auto 1fr; gap: 8px 12px; font-size: 13px; align-items: center; }
.cheat code { font: 12.5px var(--font-mono); color: var(--ink-2); background: var(--bg-sunken); padding: 2px 6px; border-radius: 4px; border: 1px solid var(--line); white-space: nowrap; }
.cheat .katex { font-size: 1.05em; }

/* ------------------------------------------------------------------ profile */

.profile-head { display: grid; grid-template-columns: auto minmax(0, 1fr) auto; gap: 22px; align-items: center; margin-bottom: 28px; }
.profile-head .avatar { --size: 96px; font-size: 36px; box-shadow: var(--shadow); }
.profile-head h1 { font: 600 32px/1.1 var(--font-serif); letter-spacing: -0.02em; }
.profile-head .handle { color: var(--ink-3); font-size: 15px; margin-top: 4px; }
.profile-head .bio { color: var(--ink-2); margin-top: 8px; max-width: 620px; }
.stat-cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(130px, 1fr)); gap: 10px; margin-bottom: 28px; }
.stat-card { padding: 14px 16px; border-radius: var(--radius); background: var(--bg-elev); border: 1px solid var(--line); }
.stat-card .stat-num { font-size: 26px; }
.answer-item { padding: 14px 2px; border-bottom: 1px solid var(--line); display: grid; grid-template-columns: 60px minmax(0, 1fr); gap: 14px; }
.answer-item .q-stats { align-items: flex-start; }

/* ------------------------------------------------------------------ leaderboard */

.leader { display: grid; grid-template-columns: 44px 40px minmax(0, 1fr) auto; gap: 14px; align-items: center; padding: 12px 14px; border-bottom: 1px solid var(--line); }
.leader:last-child { border-bottom: 0; }
.leader .rank { font: 600 20px/1 var(--font-serif); color: var(--ink-3); text-align: center; }
.leader .rank.top { width: 34px; height: 34px; border-radius: 50%; display: grid; place-items: center; margin: 0 auto; font-size: 16px; color: #3b2a00; }
.leader .rank.r1 { background: linear-gradient(140deg, #ffd96a, #e6a817); }
.leader .rank.r2 { background: linear-gradient(140deg, #eef0f4, #b6bcc8); }
.leader .rank.r3 { background: linear-gradient(140deg, #f2c29b, #c47b45); }
.leader .avatar { --size: 40px; }
.leader .name a { font-weight: 650; color: var(--ink); }
.leader .points { font: 600 18px/1 var(--font-serif); text-align: right; }
.leader .points small { display: block; font: 500 12px/1.4 var(--font-sans); color: var(--ink-3); }

/* ------------------------------------------------------------------ notifications */

.notif { display: grid; grid-template-columns: 34px minmax(0, 1fr) auto; gap: 12px; align-items: center; padding: 14px; border-bottom: 1px solid var(--line); color: var(--ink); }
.notif:hover { background: var(--bg-hover); text-decoration: none; }
.notif.unread { background: color-mix(in srgb, var(--accent-soft) 60%, transparent); }
.notif .ic { width: 34px; height: 34px; border-radius: 50%; display: grid; place-items: center; background: var(--bg-sunken); color: var(--ink-2); }
.notif .ic svg { width: 16px; height: 16px; }
.notif .ic.like { background: var(--like-soft); color: var(--like); }
.notif .ic.accept { background: var(--success-soft); color: var(--success); }
.notif .ic.answer { background: var(--accent-soft); color: var(--accent-text); }
.notif .text { font-size: 14.5px; }
.notif .text .katex { font-size: 1em; }
.notif .time { font-size: 12.5px; color: var(--ink-3); white-space: nowrap; }

/* ------------------------------------------------------------------ data page */

.data-hero { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 40px; align-items: center; margin-bottom: 30px; }
.kpis { display: grid; grid-template-columns: repeat(4, 1fr); gap: 10px; margin-bottom: 26px; }
.kpi { padding: 16px 18px; border-radius: var(--radius); background: var(--bg-elev); border: 1px solid var(--line); }
.kpi .stat-num { font-size: 30px; }
.kpi .delta { font-size: 12.5px; color: var(--ink-3); margin-top: 4px; }
.chart-grid { display: grid; grid-template-columns: minmax(0, 1.3fr) minmax(0, 1fr); gap: 18px; margin-bottom: 18px; }
.chart-card { padding: 20px; }
.chart-card h3 { font-size: 15px; font-weight: 650; }
.chart-card .sub { font-size: 13px; color: var(--ink-3); margin: 2px 0 16px; }
.kpi .stat-num, .chart-card .stat-num { font-family: var(--font-sans); font-weight: 650; letter-spacing: -0.02em; }

/* Chart palette: validated categorical slots + an ordinal blue ramp, stepped per mode. */
.viz {
  --s1: #2a78d6; --s2: #eb6834; --s3: #1baf7a;
  --o1: #86b6ef; --o2: #2a78d6; --o3: #104281;
  --meter-track: #cde2fb; --meter-fill: #2a78d6;
  --grid: var(--line);
}
@media (prefers-color-scheme: dark) {
  :root:where(:not([data-theme="light"])) .viz {
    --s1: #3987e5; --s2: #d95926; --s3: #199e70;
    --o1: #256abf; --o2: #5598e7; --o3: #9ec5f4;
    --meter-track: #0d366b; --meter-fill: #3987e5;
  }
}
:root[data-theme="dark"] .viz {
  --s1: #3987e5; --s2: #d95926; --s3: #199e70;
  --o1: #256abf; --o2: #5598e7; --o3: #9ec5f4;
  --meter-track: #0d366b; --meter-fill: #3987e5;
}

.hbar { display: grid; grid-template-columns: 150px minmax(0, 1fr); gap: 10px; align-items: center; font-size: 13px; padding: 4px 0; position: relative; }
.hbar .lbl { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; color: var(--ink-2); }
.hbar .track { display: flex; align-items: center; gap: 8px; min-width: 0; }
.hbar .bar { height: 14px; border-radius: 0 4px 4px 0; background: var(--s1); flex-shrink: 0; }
.hbar .val { font-variant-numeric: tabular-nums; color: var(--ink-2); font-weight: 600; font-size: 12.5px; }
.hbar:hover .lbl, .hbar:focus-visible .lbl { color: var(--ink); }
.hbar:hover .bar { filter: brightness(1.08); }
.legend { display: flex; gap: 16px; font-size: 12.5px; color: var(--ink-2); margin: 0 0 14px; flex-wrap: wrap; }
.legend span { display: inline-flex; align-items: center; gap: 6px; }
.legend i { width: 10px; height: 10px; border-radius: 3px; display: inline-block; }

.colchart { position: relative; height: 180px; margin-left: 30px; }
.colchart .gridline { position: absolute; left: 0; right: 0; height: 1px; background: var(--grid); }
.colchart .gridline span { position: absolute; right: calc(100% + 8px); top: -7px; font-size: 11px; color: var(--ink-3); font-variant-numeric: tabular-nums; }
.colchart .cols { position: absolute; inset: 0; display: flex; align-items: stretch; justify-content: space-between; gap: 2px; }
.colchart .col { flex: 1 1 0; display: flex; justify-content: center; align-items: flex-end; position: relative; outline: none; border-radius: 4px; }
.colchart .col:hover, .colchart .col:focus-visible { background: var(--bg-hover); }
.colchart .stack { width: 100%; max-width: 20px; display: flex; flex-direction: column-reverse; gap: 2px; }
.colchart .seg { width: 100%; }
.colchart .seg.top { border-radius: 4px 4px 0 0; }
.colchart .tip {
  position: absolute; bottom: calc(100% + 6px); left: 50%; transform: translateX(-50%); display: none; z-index: 5; pointer-events: none;
  background: var(--bg-elev); color: var(--ink); border: 1px solid var(--line); box-shadow: var(--shadow-lg);
  padding: 8px 10px; border-radius: 8px; font-size: 12px; white-space: nowrap; line-height: 1.6;
}
.colchart .tip b { display: block; margin-bottom: 2px; }
.colchart .tip i { width: 8px; height: 8px; border-radius: 2px; display: inline-block; margin-right: 6px; }
.colchart .col:hover .tip, .colchart .col:focus-visible .tip { display: block; }
.colchart .col:first-child .tip, .colchart .col:nth-child(2) .tip { left: 0; transform: none; }
.colchart .col:last-child .tip, .colchart .col:nth-last-child(2) .tip { left: auto; right: 0; transform: none; }
.axis { display: flex; justify-content: space-between; font-size: 11.5px; color: var(--ink-3); margin: 8px 0 0 30px; }
.split-bar { display: flex; height: 14px; gap: 2px; margin: 8px 0 8px; }
.split-bar span { height: 100%; }
.split-bar span:first-child { border-radius: 4px 0 0 4px; }
.split-bar span:last-child { border-radius: 0 4px 4px 0; }
.meter { height: 10px; border-radius: 5px; background: var(--meter-track); overflow: hidden; margin: 8px 0 6px; }
.meter span { display: block; height: 100%; background: var(--meter-fill); border-radius: 5px; }
.mix-row + .mix-row { margin-top: 18px; padding-top: 16px; border-top: 1px solid var(--line); }
.mix-row .row { justify-content: space-between; font-size: 13.5px; }
.table-view summary { font-size: 12.5px; color: var(--ink-3); cursor: pointer; margin-top: 12px; }
.table-view .mini-table { margin-top: 8px; }
.format-spec pre { margin: 0; }
.export-list { display: grid; gap: 8px; }
.export-item { display: flex; align-items: center; gap: 12px; padding: 10px 12px; border: 1px solid var(--line); border-radius: var(--radius-sm); background: var(--bg-elev); }
.export-item code { font: 600 13px var(--font-mono); }
.export-item .d { font-size: 13px; color: var(--ink-3); flex: 1; }
.mini-table { width: 100%; border-collapse: collapse; font-size: 13.5px; }
.mini-table td, .mini-table th { padding: 7px 4px; border-bottom: 1px solid var(--line); text-align: left; }
.mini-table th { font-size: 12px; text-transform: uppercase; letter-spacing: .05em; color: var(--ink-3); font-weight: 650; }
.mini-table td.n { text-align: right; font-variant-numeric: tabular-nums; }

/* ------------------------------------------------------------------ help */

.example-pair { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; margin-bottom: 14px; background: var(--bg-elev); }
.example-pair pre { margin: 0; padding: 14px 16px; background: var(--code-bg); font: 13px/1.6 var(--font-mono); white-space: pre-wrap; overflow-wrap: anywhere; border-right: 1px solid var(--line); }
.example-pair .out { padding: 14px 18px; }
.example-pair h4 { grid-column: 1 / -1; padding: 10px 16px; font-size: 13px; text-transform: uppercase; letter-spacing: .06em; color: var(--ink-3); border-bottom: 1px solid var(--line); background: var(--bg-sunken); }
.doc h2 { font: 600 24px/1.25 var(--font-serif); margin: 36px 0 12px; }
.doc h2:first-child { margin-top: 0; }
.doc p, .doc li { color: var(--ink-2); }
.doc ul { padding-left: 20px; }
.doc li { margin: 6px 0; }
.toc { display: grid; gap: 2px; font-size: 14px; }
.toc a { color: var(--ink-2); padding: 5px 10px; border-radius: 6px; }
.toc a:hover { background: var(--bg-hover); text-decoration: none; color: var(--ink); }

/* ------------------------------------------------------------------ auth */

.auth-wrap { min-height: calc(100vh - var(--header-h) - 200px); display: grid; place-items: center; padding-top: 40px; padding-bottom: 40px; }
.auth-card { width: 100%; max-width: 440px; padding: 32px; }
.auth-card h1 { font: 600 28px/1.2 var(--font-serif); margin-bottom: 6px; }
.auth-card .sub { color: var(--ink-3); margin-bottom: 24px; font-size: 15px; }
.auth-card .switch { text-align: center; font-size: 14px; color: var(--ink-3); margin-top: 20px; }
.consent { padding: 12px 14px; border-radius: var(--radius-sm); background: var(--bg-sunken); border: 1px solid var(--line); margin-bottom: 18px; }
.consent .checkbox { font-size: 13.5px; }

/* ------------------------------------------------------------------ menus, modals, toasts */

.menu { position: relative; }
.menu-pop {
  position: absolute; right: 0; top: calc(100% + 6px); min-width: 220px; z-index: 50; display: none;
  background: var(--bg-elev); border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow-lg); padding: 6px;
}
.menu.open .menu-pop { display: block; }
.menu-pop a, .menu-pop button {
  display: flex; align-items: center; gap: 10px; width: 100%; padding: 8px 10px; border-radius: var(--radius-sm);
  border: 0; background: none; color: var(--ink); font-size: 14px; text-align: left;
}
.menu-pop a:hover, .menu-pop button:hover { background: var(--bg-hover); text-decoration: none; }
.menu-pop svg { width: 16px; height: 16px; color: var(--ink-3); }
.menu-pop .menu-head { padding: 8px 10px 10px; border-bottom: 1px solid var(--line); margin-bottom: 4px; }
.menu-pop .menu-head b { display: block; font-size: 14.5px; }
.menu-pop .menu-head span { font-size: 12.5px; color: var(--ink-3); }
.user-btn { display: flex; align-items: center; gap: 8px; height: 38px; padding: 0 6px 0 4px; border-radius: 19px; border: 1px solid var(--line); background: var(--bg-elev); }
.user-btn:hover { border-color: var(--line-strong); }
.user-btn .avatar { --size: 30px; font-size: 12px; }
.user-btn .rep { padding-right: 6px; }

.modal-backdrop {
  position: fixed; inset: 0; z-index: 80; background: rgba(12, 14, 20, 0.45); display: grid; place-items: center; padding: 20px;
  animation: fade .15s ease-out;
}
.modal {
  width: 100%; max-width: 520px; max-height: calc(100vh - 40px); overflow: auto;
  background: var(--bg-elev); border: 1px solid var(--line); border-radius: var(--radius-lg); box-shadow: var(--shadow-lg);
  animation: rise .2s cubic-bezier(.2, .8, .2, 1);
}
.modal.wide { max-width: 860px; }
.modal-head { display: flex; align-items: center; justify-content: space-between; padding: 18px 20px 0; }
.modal-head h2 { font: 600 20px/1.3 var(--font-serif); }
.modal-body { padding: 14px 20px 6px; color: var(--ink-2); }
.modal-foot { display: flex; justify-content: flex-end; gap: 8px; padding: 14px 20px 18px; }
@keyframes fade { from { opacity: 0; } }
@keyframes rise { from { opacity: 0; transform: translateY(10px) scale(.98); } }

.revision { border: 1px solid var(--line); border-radius: var(--radius); margin-bottom: 12px; overflow: hidden; }
.revision-head { display: flex; justify-content: space-between; gap: 10px; padding: 9px 14px; background: var(--bg-sunken); font-size: 13px; color: var(--ink-3); border-bottom: 1px solid var(--line); }
.revision-body { padding: 14px; }
.revision pre { margin: 0; white-space: pre-wrap; font: 12.5px/1.6 var(--font-mono); color: var(--ink-2); }

#toasts { position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%); z-index: 90; display: grid; gap: 8px; justify-items: center; pointer-events: none; }
.toast {
  display: flex; align-items: center; gap: 10px; padding: 11px 16px; border-radius: var(--radius); pointer-events: auto;
  background: var(--ink); color: var(--bg); font-size: 14px; font-weight: 500; box-shadow: var(--shadow-lg); animation: rise .2s ease-out;
  max-width: calc(100vw - 32px);
}
.toast svg { width: 17px; height: 17px; flex-shrink: 0; }
.toast.error { background: var(--danger); color: #fff; }
.toast.out { opacity: 0; transform: translateY(8px); transition: all .25s; }

/* ------------------------------------------------------------------ footer */

.site-footer { border-top: 1px solid var(--line); padding: 40px 0 48px; color: var(--ink-3); font-size: 14px; background: var(--bg-sunken); }
.footer-grid { display: grid; grid-template-columns: 1.4fr repeat(3, 1fr); gap: 32px; }
.footer-grid h4 { font-size: 12px; text-transform: uppercase; letter-spacing: .08em; color: var(--ink-2); margin-bottom: 10px; }
.footer-grid a { display: block; color: var(--ink-3); padding: 3px 0; }
.footer-grid a:hover { color: var(--ink); }
.footer-note { margin-top: 28px; padding-top: 20px; border-top: 1px solid var(--line); font-size: 13px; display: flex; justify-content: space-between; gap: 16px; flex-wrap: wrap; }

/* ------------------------------------------------------------------ responsive */

@media (max-width: 1080px) {
  .main-nav a { padding: 7px 8px; }
  .layout, .ask-grid { grid-template-columns: minmax(0, 1fr); }
  .aside { position: static; }
  .home-cols { grid-template-columns: minmax(0, 1fr); }
  .chart-grid { grid-template-columns: minmax(0, 1fr); }
}

@media (max-width: 900px) {
  .hero-grid, .data-hero { grid-template-columns: minmax(0, 1fr); gap: 28px; }
  .formula-stack { height: 250px; max-width: 520px; }
  .layout-left { grid-template-columns: minmax(0, 1fr); }
  .facets { position: static; grid-template-columns: repeat(auto-fit, minmax(180px, 1fr)); gap: 16px; }
  .subject-row { grid-template-columns: minmax(0, 1fr); gap: 12px; }
  .kpis { grid-template-columns: repeat(2, 1fr); }
  .footer-grid { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 760px) {
  :root { --gutter: 16px; --header-h: 58px; }
  .main-nav {
    display: none; position: absolute; top: var(--header-h); left: 0; right: 0; flex-direction: column; gap: 0;
    background: var(--bg-elev); border-bottom: 1px solid var(--line); box-shadow: var(--shadow); padding: 8px var(--gutter) 12px;
  }
  .main-nav.open { display: flex; align-items: stretch; }
  .main-nav a { padding: 11px 6px; font-size: 16px; }
  .nav-more-btn { display: none; }
  .nav-more .menu-pop, .nav-more.open .menu-pop { display: contents; }
  .main-nav .theme-item { margin-top: 9px; padding: 13px 6px 11px; font-size: 16px; border-radius: var(--radius-sm); }
  .main-nav .theme-item::before { left: 0; right: 0; top: 0; }
  .icon-btn.menu-toggle { display: grid; }
  .brand-name { display: none; }
  .header-inner { gap: 8px; }
  .header-search { min-width: 0; max-width: none; }
  .header-actions .ask-btn span, .header-actions .login-btn span, .user-btn .rep { display: none; }
  .header-actions .ask-btn, .header-actions .login-btn { width: 38px; padding: 0; }
  .header-actions .login-btn svg { display: block; }
  .header-actions .signup-btn { display: none; }
  /* Signed in, "Ask a question" is in the avatar menu, so the bar keeps only the bell and avatar. */
  .header-actions:has(.user-btn) .ask-btn { display: none; }
  .hero { padding: 36px 0 32px; }
  .hero-lede { font-size: 16.5px; }
  .stats-strip { grid-template-columns: repeat(2, 1fr); }
  .stats-strip > div:nth-child(3) { border-left: 0; }
  .stats-strip > div:nth-child(n + 3) { border-top: 1px solid var(--line); }
  .ptable-group { flex: 1 1 100%; }
  .ptable { grid-auto-flow: row; grid-template-columns: repeat(auto-fill, minmax(96px, 1fr)); grid-auto-columns: auto; }
  .tile-sym { font-size: 32px; }
  .tile-name { font-size: 12px; }
  .q-item { grid-template-columns: minmax(0, 1fr); gap: 8px; }
  .q-stats { flex-direction: row; align-items: center; gap: 12px; order: 2; }
  .q-meta .by { margin-left: 0; }
  .page-title { font-size: 28px; }
  .subject-hero { grid-template-columns: 76px minmax(0, 1fr); padding: 18px; gap: 16px; }
  .subject-hero > :last-child { grid-column: 1 / -1; }
  .subject-hero .big-tile { width: 76px; height: 76px; padding: 7px 9px; }
  .big-tile .s { font-size: 32px; }
  .subject-hero h1 { font-size: 26px; }
  .form-row { grid-template-columns: minmax(0, 1fr); }
  .editor[data-view="split"] .editor-panes { grid-template-columns: minmax(0, 1fr); }
  .editor[data-view="split"] .editor-preview { border-left: 0; border-top: 1px solid var(--line); }
  .editor-views { margin-left: 0; width: 100%; padding: 4px 0 0; }
  .profile-head { grid-template-columns: auto minmax(0, 1fr); }
  .profile-head > :last-child { grid-column: 1 / -1; }
  .profile-head .avatar { --size: 68px; font-size: 26px; }
  .post-footer { flex-direction: column-reverse; align-items: stretch; }
  .author-card { min-width: 0; }
  .example-pair { grid-template-columns: minmax(0, 1fr); }
  .example-pair pre { border-right: 0; border-bottom: 1px solid var(--line); }
  .hbar { grid-template-columns: 96px minmax(0, 1fr); }
  .leader { grid-template-columns: 34px 34px minmax(0, 1fr) auto; gap: 10px; padding: 10px 6px; }
  .leader .avatar { --size: 34px; }
  .comment-children { margin-left: 4px; padding-left: 12px; }
  .footer-grid { grid-template-columns: 1fr; }
  .auth-card { padding: 22px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.01ms !important; transition-duration: 0.01ms !important; }
}
.hbar:hover { text-decoration: none; }
.footer-grid a.brand { display: flex; padding: 0; color: var(--ink); }
.doc code { font: 0.86em/1.4 var(--font-mono); background: var(--code-bg); border: 1px solid var(--line); padding: 1px 5px; border-radius: 5px; color: var(--ink); }

/* Tags index and moderation console */
.tag-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 10px; }
.tag-card {
  display: grid; gap: 6px; padding: 12px 14px; border-radius: var(--radius); background: var(--bg-elev);
  border: 1px solid var(--line); color: var(--ink); transition: border-color .15s;
}
.tag-card:hover { text-decoration: none; border-color: var(--line-strong); }
.tag-card .tag { justify-self: start; }
.tag-meta { font-size: 13px; color: var(--ink-3); }
.tag-meta b { color: var(--ink-2); }
.tag-subjects { display: flex; align-items: center; gap: 5px; font-size: 12.5px; color: var(--ink-3); flex-wrap: wrap; }
.mod-row { display: grid; grid-template-columns: auto minmax(0, 1fr) 260px; gap: 14px; align-items: start; padding: 14px 16px; border-bottom: 1px solid var(--line); }
.mod-row:last-child { border-bottom: 0; }
.mod-side { text-align: right; }
@media (max-width: 760px) {
  .mod-row { grid-template-columns: minmax(0, 1fr); }
  .mod-side { text-align: left; }
}

/* Topic search results */
.topic-result-list { border-top: 1px solid var(--line); }
.topic-result {
  display: grid; grid-template-columns: 44px minmax(0, 1fr) 20px; gap: 14px; align-items: center;
  padding: 16px 4px; border-bottom: 1px solid var(--line); color: var(--ink); transition: background .15s;
}
.topic-result:hover { text-decoration: none; background: var(--bg-hover); }
.topic-result .sym {
  width: 44px; height: 44px; border-radius: 11px; display: grid; place-items: center; align-self: start;
  background: var(--sub-bg); color: var(--sub-ink); border: 1px solid var(--sub-line); font: 600 19px/1 var(--font-serif);
}
.topic-result .body { display: grid; gap: 4px; min-width: 0; }
.topic-result .head { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.topic-result .name { font-size: 17px; font-weight: 650; }
.topic-result .desc { font-size: 14.5px; color: var(--ink-2); line-height: 1.5; }
.topic-result .meta { display: flex; gap: 14px; flex-wrap: wrap; font-size: 13px; color: var(--ink-3); }
.topic-result .meta b { color: var(--ink-2); }
.topic-result .match { display: inline-flex; align-items: center; gap: 4px; color: var(--accent-text); }
.topic-result .match svg { width: 13px; height: 13px; }
.topic-result .go { color: var(--ink-4); }
.topic-result .go svg { width: 18px; height: 18px; }
.topic-result:hover .go { color: var(--ink-2); }
@media (max-width: 900px) {
  /* On narrow screens the subject facet becomes one scrollable row of chips above the results. */
  .facets .facet h4 { margin-bottom: 6px; }
  .facets .facet-list { display: flex; gap: 6px; overflow-x: auto; scrollbar-width: none; padding-bottom: 2px; }
  .facets .facet-list::-webkit-scrollbar { display: none; }
  .facets .facet-item { flex-shrink: 0; border: 1px solid var(--line); border-radius: 16px; padding: 4px 10px; background: var(--bg-elev); }
  .facets .facet-item .n { margin-left: 4px; }
}

/* ------------------------------------------------------------------ learning hubs (topic guides, paths) */

.chip-row { display: flex; flex-wrap: wrap; gap: 6px; }
.chip-row .tag { font-family: var(--font-sans); }
.chip-row .tag button { border: 0; background: none; padding: 0 0 0 6px; color: var(--ink-3); font-size: 15px; line-height: 1; cursor: pointer; }
.chip-row .tag button:hover { color: var(--danger); }
.notice.success { background: var(--success-soft); color: var(--success); }
.mono { font-family: var(--font-mono); font-size: 14px; }
.meter { height: 6px; border-radius: 3px; background: var(--bg-sunken); overflow: hidden; border: 1px solid var(--line); }
.meter span { display: block; height: 100%; background: var(--success); border-radius: 3px; min-width: 0; }

.guide { display: grid; grid-template-columns: minmax(0, 1fr) 290px; overflow: hidden; }
.guide-main { padding: 24px 26px; min-width: 0; }
.guide-side { padding: 22px; border-left: 1px solid var(--line); background: color-mix(in srgb, var(--sub-bg) 45%, var(--bg-elev)); display: grid; gap: 20px; align-content: start; }
.guide-side .card-title { margin-bottom: 8px; }
.guide-head { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-bottom: 12px; }
.guide-head .section-title { display: inline-flex; align-items: center; gap: 9px; }
.guide-head .section-title svg { width: 21px; height: 21px; color: var(--sub-ink); }
.guide-sub { font: 650 13px/1 var(--font-sans); text-transform: uppercase; letter-spacing: .06em; color: var(--ink-3); margin: 22px 0 10px; }
.key-ideas { list-style: none; counter-reset: idea; padding: 0; margin: 0; display: grid; gap: 8px; }
.key-ideas li {
  counter-increment: idea; display: grid; grid-template-columns: 28px minmax(0, 1fr); gap: 10px; align-items: start;
  padding: 11px 14px 11px 11px; border-radius: var(--radius-sm); background: var(--bg-sunken); border: 1px solid var(--line);
}
.key-ideas li::before {
  content: counter(idea); width: 26px; height: 26px; border-radius: 50%; display: grid; place-items: center;
  background: var(--sub-solid); color: #fff; font: 650 12.5px/1 var(--font-sans); margin-top: 1px;
}
.key-ideas.compact li { padding: 8px 10px; }
.key-ideas .prose { overflow-x: auto; }
.guide-foot { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; margin-top: 16px; }
.guide-block .due { color: var(--warn); }

.path { list-style: none; padding: 0; margin: 0 0 36px; display: grid; gap: 4px; }
.path-stage { display: grid; grid-template-columns: 116px minmax(0, 1fr); gap: 16px; position: relative; }
.path.single .path-stage { grid-template-columns: minmax(0, 1fr); }
.path-stage .topic-grid { margin-bottom: 14px; }
.path-label { display: flex; flex-direction: column; align-items: flex-start; gap: 6px; padding-top: 12px; font-size: 13px; font-weight: 650; color: var(--ink-3); position: relative; }
.path-n {
  width: 30px; height: 30px; border-radius: 50%; display: grid; place-items: center; position: relative; z-index: 1;
  background: var(--sub-bg); color: var(--sub-ink); border: 1px solid var(--sub-line); font: 650 14px/1 var(--font-sans);
}
.path-stage:not(:last-child) .path-label::after {
  content: ""; position: absolute; left: 15px; top: 44px; bottom: -14px; width: 2px; background: var(--sub-line);
}
.topic-tile .after { display: flex; gap: 5px; align-items: flex-start; font-size: 12px; color: var(--ink-3); margin-top: 4px; line-height: 1.4; }
.topic-tile .after svg { width: 13px; height: 13px; flex-shrink: 0; margin-top: 1px; color: var(--sub-ink); }

/* ------------------------------------------------------------------ practice mode */

.practice { padding: 20px 22px; margin-top: 24px; border-color: var(--line-strong); }
.practice-head { display: flex; align-items: baseline; justify-content: space-between; gap: 6px 16px; flex-wrap: wrap; margin-bottom: 12px; }
.practice-head h2 { display: inline-flex; align-items: center; gap: 8px; font: 600 20px/1.2 var(--font-serif); }
.practice-head h2 svg { width: 20px; height: 20px; color: var(--warn); }
.practice-signal { font-size: 13px; color: var(--ink-3); }
.practice-mine { margin: -4px 0 12px; gap: 8px; }
.session-bar { display: flex; align-items: center; justify-content: space-between; gap: 10px; margin: -2px 0 12px; padding: 6px 10px; border-radius: var(--radius-sm); background: var(--accent-soft); color: var(--accent-text); }
.session-bar > span { display: inline-flex; align-items: center; gap: 6px; font-weight: 600; }
.session-bar svg { width: 15px; height: 15px; }
.answer-form label { display: block; font-size: 14px; font-weight: 600; margin-bottom: 6px; }
.answer-row { display: flex; gap: 8px; align-items: center; }
.answer-row .input { font-family: var(--font-mono); font-size: 15px; }
.answer-row .unit { font: 500 14px var(--font-mono); color: var(--ink-3); white-space: nowrap; }
.read-as { min-height: 30px; padding: 6px 0 2px; font-size: 14px; overflow-x: auto; overflow-y: hidden; }
.read-as .katex { font-size: 1.1em; }
.feedback .notice { margin: 10px 0 0; }
.answer-display { margin: 4px 0 2px; color: var(--ink); font-size: 15px; }
.practice-note { margin: 0 0 6px; }
.hint-list { list-style: none; padding: 0; margin: 12px 0 0; display: grid; gap: 8px; }
.hint-list:empty { display: none; }
.hint-list li { padding: 10px 14px; border-radius: var(--radius-sm); background: var(--warn-soft); border: 1px solid color-mix(in srgb, var(--warn) 22%, transparent); }
.hint-n { display: block; font-size: 12px; font-weight: 700; letter-spacing: .04em; text-transform: uppercase; color: var(--warn); margin-bottom: 2px; }
.practice-actions { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 14px; }
.rate { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; margin-top: 16px; padding-top: 14px; border-top: 1px solid var(--line); }
.rate-q { font-weight: 600; font-size: 14px; }
.rate .suggested:not([aria-pressed]) { box-shadow: inset 0 0 0 1px var(--success-line); color: var(--success); }
.practice-next { margin-top: 10px; display: grid; gap: 8px; justify-items: start; }
.practice-next p { margin: 0; }

.solutions.is-hidden [data-answers], .solutions.is-hidden .answers-sort { display: none; }
.solution-gate { display: none; }
.solutions.is-hidden .solution-gate {
  display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap;
  padding: 16px 18px; border: 1px dashed var(--line-strong); border-radius: var(--radius); color: var(--ink-2); font-size: 14.5px;
}
.solution-gate p { margin: 0; }

.practice-subjects { display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); gap: 12px; }
.practice-subject { padding: 16px; display: grid; gap: 10px; align-content: start; }
.practice-subject .name { font-weight: 650; color: var(--ink); }
.practice-subject .btn { justify-self: start; }
.tile-sym-sm {
  width: 40px; height: 40px; border-radius: 10px; display: grid; place-items: center; flex-shrink: 0;
  background: var(--sub-bg); color: var(--sub-ink); border: 1px solid var(--sub-line); font: 600 17px/1 var(--font-serif);
}
.practice-list { overflow: hidden; }
.practice-row { display: grid; grid-template-columns: 34px minmax(0, 1fr) auto; gap: 12px; align-items: center; padding: 12px 16px; border-bottom: 1px solid var(--line); color: var(--ink); }
.practice-row:last-child { border-bottom: 0; }
.practice-row:hover { background: var(--bg-hover); text-decoration: none; }
.practice-row .sym { width: 34px; height: 34px; border-radius: 9px; display: grid; place-items: center; background: var(--sub-bg); color: var(--sub-ink); border: 1px solid var(--sub-line); font: 600 14px/1 var(--font-serif); }
.practice-row .body { display: grid; gap: 3px; min-width: 0; }
.practice-row .title { font-weight: 600; font-size: 15px; }
.practice-row .meta { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; font-size: 12.5px; color: var(--ink-3); }
.stat-card .small-num { font-size: 20px; line-height: 1.5; }
.how-practice { margin-top: 40px; max-width: 760px; }
.how-practice ol { padding-left: 20px; display: grid; gap: 10px; color: var(--ink-2); margin-top: 12px; }

/* Ask form: practice fields; guide editor */
.practice-fields { border: 1px solid var(--line); border-radius: var(--radius); padding: 16px 18px 18px; margin: 0 0 18px; background: var(--bg-elev); min-width: 0; }
.practice-fields legend { display: inline-flex; align-items: center; gap: 7px; padding: 0 6px; font-size: 14.5px; font-weight: 650; }
.practice-fields legend svg { width: 17px; height: 17px; color: var(--warn); }
.practice-fields > .hint { display: block; margin: 0 0 14px; font-size: 13px; color: var(--ink-3); }
.practice-fields .err { color: var(--danger); }
.hint-editors { display: grid; gap: 10px; }
.hint-editors:empty { display: none; }
.hint-editor-head { display: flex; align-items: center; justify-content: space-between; margin-bottom: 4px; }
.hint-editor .hint-n { color: var(--ink-3); }
.guide-form { max-width: 880px; }

@media (max-width: 900px) {
  .guide { grid-template-columns: minmax(0, 1fr); }
  .guide-side { border-left: 0; border-top: 1px solid var(--line); }
}
@media (max-width: 760px) {
  .guide-main { padding: 18px 16px; }
  .guide-side { padding: 18px 16px; }
  .path-stage { grid-template-columns: minmax(0, 1fr); gap: 6px; }
  .path-label { flex-direction: row; align-items: center; padding-top: 4px; }
  .path-stage:not(:last-child) .path-label::after { display: none; }
  .practice { padding: 16px; }
  .answer-row { flex-wrap: wrap; }
  .answer-row .input { flex: 1 1 100%; }
  .answer-row .btn { flex: 1; }
  .practice-row { grid-template-columns: 34px minmax(0, 1fr); }
  .practice-row .when { grid-column: 2; }
}

/* ------------------------------------------------------------------ encyclopedia and book summaries */

.section-head-row { display: flex; align-items: flex-start; justify-content: space-between; gap: 16px; flex-wrap: wrap; }
.entry-search { max-width: 560px; height: 44px; margin-bottom: 14px; }
.entry-filters { margin-bottom: 10px; align-items: center; }
.entry-types { margin-bottom: 12px; }
.filter-chip { display: inline-flex; align-items: center; gap: 5px; height: 30px; padding: 0 12px; border-radius: 15px; border: 1px solid var(--line); background: var(--bg-elev); color: var(--ink-2); font-size: 13.5px; }
.filter-chip:hover { text-decoration: none; border-color: var(--line-strong); color: var(--ink); }
.filter-chip[aria-current="true"] { background: var(--ink); border-color: var(--ink); color: var(--bg); }
.filter-chip[aria-current="true"] .muted { color: inherit; opacity: .7; }
.entry-list { overflow: hidden; }
.entry-row { display: grid; grid-template-columns: 34px minmax(0, 1fr); gap: 12px; padding: 14px 16px; border-bottom: 1px solid var(--line); color: var(--ink); }
.entry-row:last-child { border-bottom: 0; }
.entry-letter { margin: 0; padding: 8px 16px 6px; font: 600 15px/1.2 var(--font-serif); color: var(--ink-3); background: var(--bg-sunken); border-bottom: 1px solid var(--line); }
.entry-row:hover { background: var(--bg-hover); text-decoration: none; }
.entry-icon { width: 34px; height: 34px; border-radius: 9px; display: grid; place-items: center; background: var(--bg-sunken); color: var(--ink-3); border: 1px solid var(--line); }
.entry-row.hue .entry-icon { background: var(--sub-bg); color: var(--sub-ink); border-color: var(--sub-line); }
.entry-icon svg { width: 17px; height: 17px; }
.entry-row .body { display: grid; gap: 3px; min-width: 0; }
.entry-row .title { font-weight: 650; font-size: 15.5px; }
.entry-row .by { font-size: 13.5px; color: var(--ink-3); }
.entry-row .summary { font-size: 14px; color: var(--ink-2); line-height: 1.5; }
.entry-row .meta { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; font-size: 12.5px; color: var(--ink-3); margin-top: 2px; }
.entry-list.compact .entry-row { grid-template-columns: minmax(0, 1fr); padding: 10px 0; }
.entry-list.compact .entry-icon, .entry-list.compact .summary { display: none; }
.entry-group { margin-bottom: 22px; }
.entry-group-head { display: flex; align-items: baseline; justify-content: space-between; gap: 12px; margin-bottom: 8px; }
.entry-group-head h2 { display: inline-flex; align-items: center; gap: 8px; font: 650 13px/1 var(--font-sans); text-transform: uppercase; letter-spacing: .06em; color: var(--ink-3); }
.entry-group-head h2 svg { width: 16px; height: 16px; }
.entry-group-head a { font-size: 13.5px; }
.entry-kind { display: inline-flex; align-items: center; gap: 6px; font-size: 12.5px; font-weight: 650; text-transform: uppercase; letter-spacing: .06em; color: var(--ink-3); margin-bottom: 8px; }
.entry-kind svg { width: 15px; height: 15px; }
.entry-by { margin: 6px 0 0; font-size: 16px; color: var(--ink-2); font-style: italic; }
.entry-lede { margin: 12px 0 0; font-size: 17.5px; line-height: 1.6; color: var(--ink-2); max-width: 720px; }
.entry-article > .prose { margin-top: 6px; }