/* Layout and components shared by every design. Each theme-*.css sets fonts and its own look.
   Colours follow the CS231n schedule page: cardinal red, white, warm grey panels,
   blue category bands, yellow for quizzes, red for exams. */
:root {
  --cardinal: #8c1515;
  --bg: #ffffff;
  --fg: #333333;
  --muted: #666666;
  --surface: #ffffff;
  --panel: #f7f6f1;
  --surface-2: #f5f5f5;
  --border: #dddddd;
  --accent: var(--cardinal);
  --accent-fg: #ffffff;
  --link: #3071a9;
  --band: #97afff;
  --band-fg: #1a1a1a;
  --quiz: #f5ea7f;
  --exam: #cd5c5c;
  --ok: #2e7d32;
  --ok-bg: #e8f3e8;
  --bad: #b3261e;
  --bad-bg: #f9e3e1;
  --radius: 4px;
  --font-body: system-ui, -apple-system, "Segoe UI", sans-serif;
  --font-head: var(--font-body);
  --font-ui: var(--font-body);
  --maxw: 1040px;
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-padding-top: 16px; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: var(--font-body);
  font-size: 16.5px;
  line-height: 1.6;
}
img, svg { max-width: 100%; height: auto; }
a { color: var(--link); }
h1, h2, h3 { font-family: var(--font-head); line-height: 1.25; margin: 0 0 .5em; }
h1 { font-size: clamp(1.7rem, 4vw, 2.4rem); }
h2 { font-size: 1.45rem; color: var(--accent); }
h3 { font-size: 1.08rem; }
p { margin: 0 0 1em; }
[hidden] { display: none !important; } /* keep hidden elements hidden even when a class sets display */
.sr-only { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
.muted { color: var(--muted); }

.wrap { max-width: var(--maxw); margin: 0 auto; padding: 0 16px; }
.site-main { padding: 28px 0 72px; min-height: 60vh; }

/* Header and footer */
.site-header .wrap {
  display: flex; align-items: center; justify-content: space-between;
  gap: 8px 24px; flex-wrap: wrap; padding-top: 14px; padding-bottom: 14px;
}
.brand { display: flex; flex-direction: column; line-height: 1.2; color: inherit; text-decoration: none; }
.brand-code { font-family: var(--font-head); font-weight: 700; font-size: 1.15rem; }
.brand-title { font-family: var(--font-ui); font-size: .85rem; opacity: .8; }
.site-nav { display: flex; gap: 6px 20px; flex-wrap: wrap; font-family: var(--font-ui); font-size: .95rem; }
.site-nav a { color: inherit; text-decoration: none; }
.site-nav a:hover { text-decoration: underline; }
.site-footer { font-family: var(--font-ui); font-size: .85rem; color: var(--muted); padding: 24px 0 40px; border-top: 1px solid var(--border); }
.site-footer p { margin: 0 0 .3em; }

/* Text bits */
.eyebrow {
  font-family: var(--font-ui); font-size: .76rem; font-weight: 600;
  letter-spacing: .08em; text-transform: uppercase; color: var(--muted); margin: 0 0 .4em;
}
.lead { font-size: 1.12rem; color: var(--muted); max-width: 48em; }
.section { margin-top: 48px; }
.section-note { color: var(--muted); font-size: .92rem; }
.crumbs { font-family: var(--font-ui); font-size: .9rem; margin-bottom: 18px; }
.crumbs a::before { content: "\2190\00a0"; }
.byline { text-transform: none; letter-spacing: 0; font-size: .95rem; font-weight: 600; margin-left: 4px; }
.hero-sep { opacity: .5; font-weight: 400; }
.facts { list-style: none; padding: 0; margin: 14px 0 0; display: flex; flex-wrap: wrap; gap: 6px 20px; font-family: var(--font-ui); font-size: .9rem; color: var(--muted); }

.tag, .badge {
  display: inline-block; font-family: var(--font-ui); font-size: .72rem; font-weight: 600;
  letter-spacing: .03em; padding: 2px 8px; border-radius: 999px; white-space: nowrap;
}
.tag { background: var(--surface-2); color: var(--muted); }
.badge-open { background: var(--ok-bg); color: var(--ok); }
.badge-soon { background: var(--surface-2); color: var(--muted); }

.btn {
  display: inline-block; font-family: var(--font-ui); font-size: .92rem; font-weight: 600;
  padding: 7px 16px; border-radius: var(--radius); border: 1px solid var(--accent);
  background: var(--accent); color: var(--accent-fg); text-decoration: none; cursor: pointer;
}
.btn:hover { filter: brightness(1.12); }
.btn-quiet { background: transparent; color: var(--accent); }
button:focus-visible, a:focus-visible, input:focus-visible { outline: 3px solid var(--link); outline-offset: 2px; }

.data-table { border-collapse: collapse; font-size: .95rem; }
.data-table th, .data-table td { border: 1px solid var(--border); padding: 6px 12px; text-align: left; vertical-align: top; }
.data-table th { background: var(--surface-2); font-family: var(--font-ui); font-size: .85rem; }
.table-scroll { overflow-x: auto; }

/* Schedule */
.legend { display: flex; flex-wrap: wrap; gap: 8px; margin: 0 0 12px; font-family: var(--font-ui); font-size: .8rem; }
.legend-band { background: var(--band); color: var(--band-fg); padding: 2px 10px; border-radius: 3px; font-weight: 600; }
.ev { display: inline-block; font-family: var(--font-ui); font-size: .82rem; font-weight: 600; padding: 2px 8px; border-radius: 3px; margin: 0 4px 4px 0; color: var(--band-fg); }
.ev-quiz { background: var(--quiz); }
.ev-exam { background: var(--exam); }
.schedule { width: 100%; border-collapse: collapse; font-size: .95rem; }
.schedule th { text-align: left; font-family: var(--font-ui); font-size: .85rem; background: var(--surface-2); padding: 10px 12px; border-bottom: 2px solid var(--border); }
.schedule td { padding: 10px 12px; vertical-align: top; border-bottom: 1px solid var(--border); }
.schedule .wk { width: 5.5em; white-space: nowrap; }
.schedule .wk strong { font-size: 1.05rem; }
.schedule .date { display: block; font-size: .8rem; color: var(--muted); }
.schedule td:nth-child(3) { width: 13em; font-size: .9rem; }
.schedule td:nth-child(4) { width: 11em; }
.band td { background: var(--band); color: var(--band-fg); font-family: var(--font-ui); font-weight: 700; padding: 7px 12px; }
.band a { color: inherit; }
.band-meta { font-weight: 500; font-size: .85rem; opacity: .85; margin-left: 6px; }
.band-revision td { background: var(--surface-2); }
.band-exam td { background: var(--exam); }
.row-ch { font-family: var(--font-ui); font-size: .75rem; font-weight: 700; color: var(--muted); margin-right: 4px; }
.row-revision td { color: var(--muted); }

@media (max-width: 680px) {
  .schedule thead { display: none; }
  .schedule, .schedule tbody, .schedule tr, .schedule td { display: block; width: 100%; }
  .schedule tr.row { padding: 8px 0; border-bottom: 1px solid var(--border); }
  .schedule tr.row td { border: 0; padding: 2px 4px; width: auto; }
  .schedule tr.row td:empty { display: none; }
  .schedule tr.row td.wk::before { content: "Week "; font-weight: 700; }
  .schedule td.wk .date { display: block; }
  .schedule td[data-label="Materials"]:not(:empty)::before { content: "Materials: "; font-weight: 600; color: var(--muted); }
}

/* Chapter list */
.chapter-list { list-style: none; padding: 0; margin: 0; }
.ch-link { display: flex; align-items: baseline; gap: 6px 16px; flex-wrap: wrap; color: inherit; text-decoration: none; }
.ch-num { font-family: var(--font-ui); font-size: .8rem; font-weight: 700; color: var(--accent); text-transform: uppercase; letter-spacing: .05em; }
.ch-title { font-family: var(--font-head); font-weight: 600; font-size: 1.06rem; }
a.ch-link .ch-title { color: var(--link); }
.ch-meta { display: inline-flex; gap: 6px; align-items: center; flex-wrap: wrap; }
.ch-weeks { font-family: var(--font-ui); font-size: .82rem; font-weight: 600; color: var(--fg); }
.is-soon .ch-title { color: var(--muted); }

.lanes { display: grid; grid-template-columns: repeat(auto-fit, minmax(260px, 1fr)); gap: 20px; }
.lane h3 { margin-bottom: .4em; }
.lane p:last-child { margin-bottom: 0; }

.about { max-width: 52em; }
.info-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(260px, 1fr)); gap: 20px 32px; margin: 16px 0 8px; }
.clo-head { margin-top: 24px; }
.clo-list, .lp-list { list-style: none; padding: 0; margin: 0; }
.clo-list li, .lp-list li { display: flex; gap: 14px; padding: 9px 0; border-bottom: 1px solid var(--border); }
.clo-id, .lp-id { flex: 0 0 auto; min-width: 3.2em; font-family: var(--font-ui); font-weight: 700; font-size: .85rem; color: var(--accent); padding-top: .15em; }

/* Chapter page */
.chapter-head { margin-bottom: 8px; }
.chapter-top { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 24px; margin-top: 28px; }
.chapter-top h2 { font-size: 1.15rem; }
.when, .materials-box { background: var(--panel); padding: 18px 20px; border-radius: var(--radius); }
.when-list { list-style: none; padding: 0; margin: 0 0 10px; }
.when-list li { display: flex; flex-direction: column; padding: 6px 0; border-bottom: 1px solid var(--border); }
.when-wk { font-family: var(--font-ui); font-weight: 700; font-size: .85rem; color: var(--accent); }
.when-quiz { margin: 10px 0 0; font-size: .95rem; }
.materials { list-style: none; padding: 0; margin: 0 0 14px; }
.material { display: flex; align-items: center; gap: 8px 14px; flex-wrap: wrap; padding: 8px 0; border-bottom: 1px solid var(--border); }
.material-part { list-style: none; padding: 12px 0 2px; font-family: var(--font-ui); font-size: .82rem; font-weight: 700; color: var(--accent); }
.material-part:first-child { padding-top: 0; }
.part-head h2 { background: var(--band); color: var(--band-fg); padding: 8px 14px; border-radius: var(--radius); font-size: 1.25rem; }
.part-head .lead { margin-top: 8px; }
.material-kind { font-family: var(--font-ui); font-size: .72rem; font-weight: 700; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); min-width: 4.2em; }
.material-label { flex: 1; font-weight: 600; min-width: 10em; }
.material .btn { padding: 4px 12px; font-size: .85rem; }
.sheet-card + .sheet-card { margin-top: 12px; }
.sheet-card { display: flex; flex-direction: column; gap: 4px; align-items: flex-start; padding: 16px; border: 1px solid var(--border); border-radius: var(--radius); background: var(--surface); color: inherit; text-decoration: none; }
.sheet-card strong { font-family: var(--font-head); font-size: 1.12rem; color: var(--link); }
.sheet-card .btn { margin-top: 8px; }
.prose ul { padding-left: 1.2em; max-width: 52em; }
.prose li { margin-bottom: .5em; }
.checklist { list-style: none; padding: 0; margin: 0; }
.checklist label { display: flex; gap: 12px; align-items: flex-start; padding: 8px 0; border-bottom: 1px solid var(--border); cursor: pointer; }
.checklist input { width: 18px; height: 18px; margin-top: .2em; accent-color: var(--ok); flex: 0 0 auto; }
.checklist input:checked + span { color: var(--muted); text-decoration: line-through; }

/* Practice sheet */
.rules { padding-left: 1.2em; margin: 16px 0; max-width: 52em; }
.rules li { margin-bottom: .35em; }
.coverage { margin: 20px 0 8px; font-family: var(--font-ui); }
.coverage summary { cursor: pointer; font-weight: 600; color: var(--link); }
.coverage .lp-list { font-family: var(--font-body); margin-top: 8px; }
.lp-qs a { font-family: var(--font-ui); font-size: .78rem; font-weight: 700; margin-right: 6px; }

.questions { display: flex; flex-direction: column; gap: 24px; margin-top: 24px; }
.q { scroll-margin-top: 16px; }
.q-head { display: flex; align-items: center; gap: 8px 10px; flex-wrap: wrap; margin-bottom: 10px; font-family: var(--font-ui); }
.q-num { font-weight: 800; font-size: 1.05rem; color: var(--accent); }
.q-title { font-weight: 700; }
.q-format { font-size: .7rem; font-weight: 700; text-transform: uppercase; letter-spacing: .06em; padding: 2px 8px; border-radius: 3px; background: var(--band); color: var(--band-fg); }
.q-status { color: var(--ok); font-weight: 800; }
.conf { margin-left: auto; display: inline-flex; border: 1px solid var(--border); border-radius: 999px; overflow: hidden; }
.conf button { font: 600 .75rem var(--font-ui); padding: 3px 10px; border: 0; background: var(--surface); color: var(--muted); cursor: pointer; }
.conf button + button { border-left: 1px solid var(--border); }
.conf button[data-conf="S"][aria-pressed="true"] { background: var(--ok-bg); color: var(--ok); }
.conf button[data-conf="U"][aria-pressed="true"] { background: var(--quiz); color: var(--band-fg); }
.q-prompt blockquote { margin: 10px 0; padding: 8px 14px; border-left: 3px solid var(--border); color: var(--muted); font-style: italic; }
.q-fig { margin: 10px 0; color: var(--fg); overflow-x: auto; }
.q-fig svg { display: block; }
.q-table { overflow-x: auto; margin: 8px 0; }
.work { margin: 12px 0; padding: 10px 14px 10px 40px; background: var(--panel); border-radius: var(--radius); }
.work li { padding: 3px 0; }
.work li::marker { font-family: var(--font-ui); font-weight: 700; color: var(--muted); }
.hint { font-size: .95rem; color: var(--muted); }

.tier { margin-top: 14px; }
.tier-note { margin: 0; color: var(--muted); font-size: .95rem; font-style: italic; }
.tier-label { font-family: var(--font-ui); font-weight: 700; font-size: .9rem; margin-bottom: 6px; }
.opts { display: flex; flex-direction: column; gap: 6px; }
.opt {
  display: flex; align-items: flex-start; gap: 10px; padding: 7px 12px; cursor: pointer;
  border: 1px solid var(--border); border-radius: var(--radius); background: var(--surface);
}
.opt input { margin: .35em 0 0; accent-color: var(--accent); flex: 0 0 auto; }
.opt-letter { font-family: var(--font-ui); font-weight: 700; color: var(--muted); min-width: 1.6em; }
.opt-text { flex: 1; }
.opt:has(input:checked) { border-color: var(--link); }
.opt.is-right { border-color: var(--ok); background: var(--ok-bg); }
.opt.is-wrong { border-color: var(--bad); background: var(--bad-bg); }
.part-mark { margin: 4px 0 0; font-family: var(--font-ui); font-size: .85rem; font-weight: 600; }
.part-mark:empty { display: none; }
.part-mark.is-ok { color: var(--ok); }
.part-mark.is-bad { color: var(--bad); }

.num { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; font-family: var(--font-ui); }
.num input { width: 9em; padding: 7px 10px; font: inherit; font-size: 1rem; border: 1px solid var(--border); border-radius: var(--radius); background: var(--surface); color: var(--fg); }

.q-actions { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 14px; }
.feedback { margin-top: 10px; font-family: var(--font-ui); font-size: .95rem; }
.feedback:empty { display: none; }
.feedback.is-ok, .feedback.is-bad { padding: 8px 12px; border-radius: var(--radius); }
.feedback.is-ok { background: var(--ok-bg); color: var(--ok); }
.feedback.is-bad { background: var(--bad-bg); color: var(--bad); }
.explain { margin-top: 12px; padding: 12px 14px; border-left: 3px solid var(--accent); background: var(--panel); border-radius: 0 var(--radius) var(--radius) 0; }

.scorebar { position: sticky; bottom: 0; background: var(--surface); border-top: 1px solid var(--border); font-family: var(--font-ui); font-size: .9rem; z-index: 5; }
.scorebar-inner { display: flex; align-items: center; gap: 8px 16px; padding-top: 10px; padding-bottom: 10px; flex-wrap: wrap; }
.score-track { flex: 1; min-width: 80px; height: 8px; background: var(--surface-2); border-radius: 99px; overflow: hidden; }
#score-bar { display: block; height: 100%; width: 0; background: var(--ok); transition: width .3s; }
.unsure-list a { font-weight: 700; margin-left: 4px; }
.page-sheet .site-main { padding-bottom: 24px; }

.katex { font-size: 1.05em; }

@media (max-width: 600px) {
  body { font-size: 16px; }
  .section { margin-top: 40px; }
  .conf { margin-left: 0; }
}

/* Topics page */
.topic-group h2 a { color: inherit; text-decoration: none; }
.topic-group h2 a:hover { text-decoration: underline; }
.topic-list { list-style: none; padding: 0; margin: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 8px 24px; }
.topic-list li { display: flex; justify-content: space-between; align-items: baseline; gap: 12px; padding: 8px 0; border-bottom: 1px solid var(--border); }
.topic-name { font-weight: 600; }
.topic-practice { font-family: var(--font-ui); font-size: .82rem; white-space: nowrap; }
.site-footer .license { margin-top: .6em; max-width: 60em; }

/* Home page QR code */
.hero { display: flex; align-items: center; justify-content: space-between; gap: 24px 32px; }
.hero-text { min-width: 0; }
.hero-qr { flex: 0 0 auto; margin: 0; text-align: center; font-family: var(--font-ui); font-size: .8rem; line-height: 1.4; }
.hero-qr img { display: block; width: 150px; height: 150px; margin: 0 auto 8px; padding: 6px; background: #fff; border-radius: 10px; }
.hero-qr a { color: inherit; }
@media (max-width: 720px) { .hero-qr { display: none; } }

/* Full-screen QR code panel (menu: "QR code") */
.qr-panel { display: none; position: fixed; inset: 0; z-index: 1000; background: rgba(0, 0, 0, .78); align-items: center; justify-content: center; padding: 16px; overflow-y: auto; }
.qr-panel:target:not(.is-closed) { display: flex; }
.qr-box { background: #fff; color: #1a1a1a; border-radius: 16px; padding: 24px 20px; width: 100%; max-width: 440px; text-align: center; margin: auto; }
.qr-box .eyebrow { color: var(--cardinal); }
.qr-box h2 { font-size: 1.3rem; color: #1a1a1a; margin-bottom: 12px; }
.qr-box img { display: block; width: min(78vw, 60vh, 360px); height: auto; aspect-ratio: 1; margin: 0 auto 12px; }
.qr-url { font-family: var(--font-ui); font-weight: 800; font-size: 1.15rem; margin: 0 0 6px; word-break: break-all; }
.qr-hint { color: #555; font-size: .92rem; margin: 0 0 16px; }
.qr-actions { display: flex; gap: 10px; justify-content: center; flex-wrap: wrap; }
.qr-actions .btn { min-width: 8em; }
.qr-status { margin: 10px 0 0; font-family: var(--font-ui); font-size: .85rem; color: var(--ok); }
.qr-status:empty { display: none; }