:root {
  color-scheme: dark;
  --bg: #0b0e0c;
  --surface: #101411;
  --surface-strong: #151a16;
  --ink: #f3f6f2;
  --muted: #a0aaa1;
  --quiet: #727b73;
  --accent: #63e68c;
  --accent-ink: #071109;
  --line: #252c26;
  --line-strong: #3a433b;
  --max-width: 1220px;
  --radius: 18px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  min-width: 320px;
  background: var(--bg);
  color: var(--ink);
  font-family: Inter, ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.6;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}
a { color: inherit; }
button, input { font: inherit; }
.shell { width: min(calc(100% - 48px), var(--max-width)); margin-inline: auto; }
.skip-link { position: fixed; top: 12px; left: 12px; z-index: 20; padding: 10px 14px; background: var(--accent); color: var(--accent-ink); transform: translateY(-180%); }
.skip-link:focus { transform: translateY(0); }
.visually-hidden { position: absolute; width: 1px; height: 1px; padding: 0; overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0; }

.site-header { position: relative; z-index: 10; border-bottom: 1px solid var(--line); background: rgba(11, 14, 12, 0.88); backdrop-filter: blur(16px); }
.header-inner { min-height: 76px; display: flex; align-items: center; justify-content: space-between; gap: 28px; }
.brand { display: flex; align-items: baseline; gap: 12px; text-decoration: none; }
.brand-name { font-size: 1.06rem; font-weight: 780; letter-spacing: -0.04em; }
.brand-note, .eyebrow, .collection-label, .course-domain, .course-index { font-family: "SFMono-Regular", Consolas, monospace; text-transform: uppercase; letter-spacing: 0.11em; }
.brand-note { color: var(--quiet); font-size: 0.65rem; }
.header-nav { display: flex; gap: 24px; color: var(--muted); font-size: 0.78rem; }
.header-nav a { text-decoration: none; }
.header-nav a:hover { color: var(--ink); }

.hero { min-height: 680px; padding-block: clamp(72px, 10vw, 132px) 92px; display: grid; grid-template-columns: minmax(0, 1.55fr) minmax(300px, .72fr); align-items: end; gap: clamp(56px, 9vw, 128px); }
.eyebrow { margin: 0; color: var(--accent); font-size: 0.7rem; font-weight: 750; }
.hero h1 { max-width: 850px; margin: 20px 0 26px; font-size: clamp(3.6rem, 8.4vw, 7.6rem); font-weight: 680; line-height: .91; letter-spacing: -0.078em; text-wrap: balance; }
.hero-lede { max-width: 700px; margin: 0; color: var(--muted); font-size: clamp(1.02rem, 1.6vw, 1.2rem); line-height: 1.8; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 34px; }
.button { min-height: 48px; display: inline-flex; align-items: center; justify-content: center; padding: 0 19px; border: 1px solid transparent; border-radius: 10px; font-size: .86rem; font-weight: 740; text-decoration: none; transition: transform 160ms ease, border-color 160ms ease, background 160ms ease; }
.button:hover { transform: translateY(-2px); }
.button-primary { background: var(--accent); color: var(--accent-ink); }
.button-secondary { border-color: var(--line-strong); color: var(--muted); }
.button-secondary:hover { border-color: var(--muted); color: var(--ink); }
.collection-note { padding-top: 25px; border-top: 3px solid var(--accent); }
.collection-label { margin: 0; color: var(--quiet); font-size: .66rem; }
.collection-quote { margin: 19px 0 28px; font-size: clamp(1.35rem, 2.6vw, 2.05rem); font-weight: 580; line-height: 1.28; letter-spacing: -.04em; }
.collection-stats { display: grid; grid-template-columns: repeat(3, 1fr); margin: 0; border: 1px solid var(--line); border-radius: 12px; overflow: hidden; }
.collection-stats div { min-width: 0; padding: 15px; background: var(--surface); }
.collection-stats div + div { border-left: 1px solid var(--line); }
.collection-stats dt { font-size: 1.35rem; font-weight: 760; }
.collection-stats dd { margin: 3px 0 0; color: var(--quiet); font-size: .67rem; white-space: nowrap; }

.principles { border-block: 1px solid var(--line); background: var(--surface); }
.principle-grid { display: grid; grid-template-columns: repeat(3, 1fr); }
.principle-grid article { position: relative; min-height: 220px; padding: 38px 38px 42px 0; }
.principle-grid article + article { padding-left: 38px; border-left: 1px solid var(--line); }
.principle-grid span { color: var(--accent); font-family: "SFMono-Regular", Consolas, monospace; font-size: .72rem; }
.principle-grid h2 { margin: 54px 0 9px; font-size: 1.1rem; letter-spacing: -.025em; }
.principle-grid p { max-width: 310px; margin: 0; color: var(--muted); font-size: .84rem; }

.library { padding-block: 92px 120px; }
.library-heading { display: flex; align-items: end; justify-content: space-between; gap: 36px; margin-bottom: 34px; }
.library-heading h2 { margin: 12px 0 0; font-size: clamp(2.2rem, 4.8vw, 4.4rem); line-height: 1; letter-spacing: -.064em; }
.library-heading > p { max-width: 430px; margin: 0; color: var(--muted); font-size: .88rem; }
.library-tools { display: flex; align-items: center; gap: 18px; padding-block: 20px; border-block: 1px solid var(--line-strong); }
.search-field { flex: 1; }
.search-field input { width: 100%; min-height: 46px; padding: 0 15px; border: 1px solid var(--line); border-radius: 9px; outline: 0; background: var(--surface); color: var(--ink); }
.search-field input::placeholder { color: var(--quiet); }
.search-field input:focus { border-color: var(--accent); box-shadow: 0 0 0 3px rgba(99, 230, 140, .1); }
.filters { display: flex; flex-wrap: wrap; gap: 8px; justify-content: flex-end; }
.filter-button { min-height: 36px; padding: 0 12px; border: 1px solid var(--line); border-radius: 999px; background: transparent; color: var(--muted); cursor: pointer; font-size: .73rem; }
.filter-button:hover, .filter-button[aria-pressed="true"] { border-color: var(--accent); color: var(--ink); background: rgba(99, 230, 140, .08); }
.results-note { margin: 18px 0 0; color: var(--quiet); font-family: "SFMono-Regular", Consolas, monospace; font-size: .67rem; text-transform: uppercase; letter-spacing: .09em; }
.course-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 1px; margin-top: 18px; border: 1px solid var(--line); background: var(--line); }
.course-card { --course-accent: var(--accent); position: relative; min-height: 330px; display: flex; flex-direction: column; padding: clamp(26px, 4vw, 42px); overflow: hidden; background: var(--bg); text-decoration: none; transition: background 180ms ease; }
.course-card::before { position: absolute; inset: 0 auto 0 0; width: 3px; background: var(--course-accent); content: ""; transform: scaleY(0); transform-origin: bottom; transition: transform 200ms ease; }
.course-card:hover, .course-card:focus-visible { background: var(--surface-strong); outline: none; }
.course-card:hover::before, .course-card:focus-visible::before { transform: scaleY(1); }
.course-card-top { display: flex; align-items: center; justify-content: space-between; gap: 20px; }
.course-code { font-size: .94rem; font-weight: 780; letter-spacing: -.02em; }
.course-index { color: var(--quiet); font-size: .63rem; }
.course-domain { margin: auto 0 11px; color: var(--course-accent); font-size: .64rem; font-weight: 700; }
.course-title { margin: 0; font-size: clamp(1.5rem, 2.8vw, 2.35rem); line-height: 1.05; letter-spacing: -.052em; }
.course-title-zh { display: block; margin-top: 9px; color: var(--muted); font-size: .9rem; font-weight: 500; letter-spacing: -.01em; }
.course-summary { max-width: 540px; margin: 18px 0 26px; color: var(--muted); font-size: .86rem; }
.course-meta { display: flex; flex-wrap: wrap; align-items: center; gap: 7px 14px; padding-top: 18px; border-top: 1px solid var(--line); color: var(--quiet); font-family: "SFMono-Regular", Consolas, monospace; font-size: .66rem; }
.course-meta strong { color: var(--ink); font-weight: 650; }
.course-tags { display: flex; flex-wrap: wrap; gap: 7px; margin-top: 15px; }
.course-tag { padding: 4px 8px; border: 1px solid var(--line); border-radius: 999px; color: var(--quiet); font-size: .64rem; }
.empty-state, .load-error { grid-column: 1 / -1; padding: 44px; border: 1px solid var(--line); color: var(--muted); background: var(--surface); }

.site-footer { border-top: 1px solid var(--line); }
.footer-inner { min-height: 150px; display: flex; align-items: center; justify-content: space-between; gap: 40px; }
.footer-inner strong { font-size: .95rem; }
.footer-inner p { margin: 5px 0 0; color: var(--quiet); font-size: .75rem; }
.footer-links { display: flex; gap: 24px; color: var(--muted); font-size: .76rem; }
.footer-links a { text-decoration: none; }
.footer-links a:hover { color: var(--ink); }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 4px; }

@media (max-width: 900px) {
  .hero { min-height: 0; grid-template-columns: 1fr; }
  .collection-note { max-width: 680px; }
  .library-heading { align-items: start; flex-direction: column; }
  .library-tools { align-items: stretch; flex-direction: column; }
  .filters { justify-content: flex-start; }
  .course-grid { grid-template-columns: 1fr; }
}
@media (max-width: 680px) {
  .shell { width: min(calc(100% - 32px), var(--max-width)); }
  .header-inner { min-height: 68px; }
  .brand-note, .header-nav a:not(:first-child) { display: none; }
  .hero { padding-block: 62px 68px; }
  .hero h1 { font-size: clamp(3rem, 17vw, 5.25rem); }
  .hero-actions { align-items: stretch; flex-direction: column; }
  .collection-stats { grid-template-columns: 1fr; }
  .collection-stats div + div { border-top: 1px solid var(--line); border-left: 0; }
  .principle-grid { grid-template-columns: 1fr; }
  .principle-grid article { min-height: 0; padding: 30px 0; }
  .principle-grid article + article { padding-left: 0; border-top: 1px solid var(--line); border-left: 0; }
  .principle-grid h2 { margin-top: 28px; }
  .library { padding-block: 68px 80px; }
  .course-card { min-height: 300px; }
  .footer-inner { align-items: flex-start; flex-direction: column; justify-content: center; }
  .footer-links { flex-wrap: wrap; gap: 12px 20px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition-duration: .01ms !important; }
}