/* Platform tokens mirror assets/platform.css without importing its global layout. */
:root{
  --bg:#fff;--soft:#f5f7fb;--ink:#111827;--sub:#4b5565;--mute:#6b7280;--line:#e5e8ef;
  --brand:#3d5afe;--brand-d:#2639c9;--brand-soft:#eef1ff;--brand-ink:#24319a;
  --warn:#8a5a00;--warn-soft:#fff4d6;--ok:#0b7a4f;--ok-bg:#16a06a;--ok-soft:#e6f6ee;--bad:#c2362f;--bad-soft:#fdecec;--grape:#5b3fd6;
  --sans:-apple-system,BlinkMacSystemFont,"Helvetica Neue","PingFang SC","Hiragino Sans GB","Microsoft YaHei",sans-serif;
}

*{box-sizing:border-box}
body{margin:0;background:var(--bg);color:var(--ink);font:16px/1.7 var(--sans);-webkit-font-smoothing:antialiased}
a{color:var(--brand-ink);text-decoration:none}
button,input,select{font:inherit}
button{cursor:pointer}
button,a,input,select{touch-action:manipulation}
main{max-width:1280px;margin:auto;padding:20px 32px 64px;min-width:0}
.breadcrumbs{font-size:12px;color:var(--sub);margin-bottom:16px}
.breadcrumbs a{color:var(--sub)}
h1{font-size:clamp(28px,3.3vw,44px);letter-spacing:-.03em;line-height:1.25;margin:0 0 12px}
h2{font-size:23px;line-height:1.4}
h3{font-size:18px;line-height:1.5}
.catalog-hero{padding:4px 0 24px}
.intro{font-size:16px;color:var(--sub);margin:0;max-width:52em}
.filters{display:flex;flex-wrap:wrap;align-items:flex-end;gap:12px;padding:16px 0;margin-bottom:24px;border-top:1px solid var(--line);border-bottom:1px solid var(--line);background:var(--bg)}
.filters label{display:flex;flex-direction:column;gap:4px;font-size:12px;color:var(--sub);min-width:0}
.filters .search-field{flex:1 1 100%}
.filters .search-field input{width:100%;min-width:0}
.filters .subject-tabs{flex-basis:100%;flex-wrap:wrap}
.filters select{max-width:100%}
.subject-tabs{display:flex;gap:4px;flex-shrink:0}
.filters button,.filters select,.filters input{border:1px solid var(--line);border-radius:12px;background:var(--bg);color:var(--sub);height:40px;padding:0 12px;font-size:13px;flex-shrink:0}
.subject-tabs button{border-color:transparent;font-weight:600;white-space:nowrap}
.subject-tabs span{margin-left:3px;font-size:12px}
.subject-tabs button[aria-pressed=true]{background:var(--brand-ink);color:white}
.filters input{min-width:160px;width:220px;flex:1}
.filters input::placeholder{color:var(--sub)}
#course-count{font-size:12px;white-space:nowrap;color:var(--sub);margin-left:auto}
.course-group{margin-bottom:42px}
.group-heading{display:flex;align-items:center;justify-content:space-between;gap:16px;margin-bottom:16px}
.group-heading h2{margin:0;display:flex;align-items:center;gap:16px}
.group-heading h2 span,.group-heading>span{color:var(--sub);font-size:13px;font-weight:400}
.course-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:24px}
.course{position:relative;display:flex;flex-direction:column;min-width:0;border:1px solid var(--line);border-radius:16px;background:var(--bg);transition:transform .18s,box-shadow .18s}
.course:hover{transform:translateY(-3px);box-shadow:0 6px 18px rgba(17,24,39,.08)}
.course-link{display:flex;flex-direction:column;flex:1;color:var(--ink);border-radius:16px}
.course-image{position:relative;margin:8px 8px 0;border-radius:12px;overflow:hidden;background:var(--soft)}
.course-image img{display:block;width:100%;height:auto;aspect-ratio:16/10;object-fit:cover}
.subject,.grade-label{position:absolute;top:10px;padding:3px 10px;border-radius:8px;font-size:12px;font-weight:600}
.subject{left:10px;color:white;background:var(--brand-ink)}
.subject.yingyu{background:var(--ok)}
.subject.lishi{background:var(--bad)}
.grade-label{right:10px;background:var(--bg);color:var(--sub)}
.course-copy{padding:14px 18px 18px;flex:1}
.course h3{margin:0 0 6px}
.description{font-size:14px;line-height:1.65;color:var(--sub);margin:0 0 14px;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden;min-height:46px}
.concepts{display:flex;gap:6px;flex-wrap:wrap}
.concepts span{font-size:11px;background:var(--soft);color:var(--sub);padding:2px 8px;border-radius:6px}
.versions{display:flex;gap:8px;flex-wrap:wrap;padding:0 18px 18px}
.versions a{border:1px solid var(--line);border-radius:8px;padding:4px 9px;font-size:12px;background:var(--brand-soft);color:var(--brand-ink)}
.versions a:hover{text-decoration:underline}
.featured .course-grid{grid-template-columns:repeat(6,minmax(0,1fr))}
.featured .course{grid-column:span 2;background:var(--soft)}
.featured .course:nth-child(n+4){grid-column:span 3}
.featured .course-copy{padding:16px 20px 22px}
.featured h3{font-size:18px}
.featured .concepts span{background:var(--bg)}
.collection-links{display:flex;flex-wrap:wrap;gap:16px 24px;border-top:1px solid var(--line);padding:24px 0;font-size:14px}
.collection-links>span{color:var(--sub)}
.guide{margin:32px 0;max-width:960px}
.guide h2{font-size:22px}
.guide details{border-bottom:1px solid var(--line);padding:16px 0}
.guide summary{cursor:pointer;font-weight:600;font-size:15px}
.guide p,.guide li{font-size:14px;color:var(--sub)}
.lesson-hero{display:grid;grid-template-columns:1fr 1fr;gap:32px;align-items:center;padding:12px 0 24px}
.eyebrow{font-size:13px;color:var(--brand-ink);margin:0 0 14px}
.lesson-hero h1{font-size:clamp(28px,3vw,40px)}
.lesson-preview{position:relative;display:block;border:1px solid var(--line);border-radius:16px;padding:8px;background:var(--soft)}
.lesson-preview img{width:100%;height:auto;display:block;border-radius:12px}
.lesson-preview span{display:block;text-align:center;padding:8px;font-size:14px;font-weight:600}
.lesson-actions{display:flex;flex-wrap:wrap;gap:12px;margin:24px 0 12px}
.primary,.lesson-actions button{border:1px solid var(--brand-ink);border-radius:12px;padding:10px 18px;background:var(--bg);color:var(--brand-ink);font-size:14px}
.primary{background:var(--brand-ink);color:white}
.hint,.placement{font-size:12px;color:var(--sub)}
.placement:empty{display:none}
#lesson-player{grid-column:1/-1}
#lesson-player:empty{display:none}
.lesson-columns{display:grid;grid-template-columns:1.3fr 1fr;gap:40px;margin:24px 0}
.lesson-columns aside{background:var(--soft);padding:24px;border-radius:16px}
.lesson-columns h2{font-size:21px}
.lesson-columns dt{font-size:12px;color:var(--sub);margin-top:12px}
.lesson-columns dd{margin:0}
iframe{width:100%;height:75vh;min-height:480px;border:1px solid var(--line);border-radius:12px}
#course-empty{padding:64px 20px;text-align:center;background:var(--soft);border-radius:16px}
[hidden]{display:none!important}
:focus-visible{outline:3px solid var(--brand-ink);outline-offset:3px}
.skip{position:absolute;left:16px;top:-80px;background:white;padding:12px;z-index:99}
.skip:focus{top:8px}
.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip-path:inset(50%);white-space:nowrap;border:0}

@media(max-width:1099px){.course-grid,.featured .course-grid{grid-template-columns:repeat(2,minmax(0,1fr));gap:20px}
.featured .course,.featured .course:nth-child(n+4){grid-column:auto}
.filters{gap:8px}
.group-heading h2{align-items:baseline;flex-wrap:wrap;gap:6px 14px}
}

@media(max-width:599px){main{padding:16px 16px 40px}
.breadcrumbs{margin-bottom:14px}
.catalog-hero{padding-bottom:18px}
.intro{font-size:14px}
.filters{margin-bottom:20px}
.course-grid,.featured .course-grid{grid-template-columns:minmax(0,1fr)}
.group-heading{align-items:flex-start}
.group-heading h2{font-size:21px;display:block}
.group-heading h2 span{display:block;margin-top:4px;font-size:12px}
.group-heading>span{white-space:nowrap;font-size:12px}
.course-group{margin-bottom:32px}
.lesson-hero,.lesson-columns{grid-template-columns:1fr;gap:20px}
.lesson-preview{grid-row:2}
.lesson-hero h1{font-size:28px}
.lesson-columns aside{padding:20px}
}

@media(prefers-reduced-motion:reduce){*,*::before,*::after{scroll-behavior:auto!important;transition:none!important;animation:none!important}
.course:hover{transform:none}
}


.preview-unavailable{aspect-ratio:16/10;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:8px;background:var(--soft);color:var(--sub);border-radius:12px;font-size:13px}
.preview-unavailable strong{font-size:16px;font-weight:500}

/* Textbook entry shares the catalogue's typography and responsive layout. */
.curriculum-nav{border:1px solid var(--line);border-radius:12px;padding:18px 20px;margin:0 0 24px;background:var(--soft);display:flex;flex-wrap:wrap;gap:10px 24px;font-size:14px}
.curriculum-nav>div{display:flex;flex-wrap:wrap;gap:10px 24px;flex-basis:100%}
.placement{font-size:12px;color:var(--sub);line-height:1.7}
.group-heading h2{flex-wrap:wrap}
@media(max-width:599px){.filters label:not(.search-field){flex:1 1 40%}.filters label select{width:100%;padding:0 8px}.subject-tabs button{padding:0 10px}#course-count{align-self:center}}