:root {
  color-scheme: light;
  --ink: #171717;
  --muted: #686868;
  --paper: #f7f5ef;
  --surface: #fffef9;
  --line: #dedbd1;
  --accent: #fbbf24;
  --accent-soft: #fff1bd;
  --success: #16794a;
  --danger: #b42318;
  --shadow: 0 18px 50px rgba(23, 23, 23, .08);
  --radius: 18px;
  --max: 1180px;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(circle at 82% 5%, rgba(251,191,36,.20), transparent 27rem),
    var(--paper);
  font: 16px/1.65 ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
}
a { color: inherit; }
button, input, select { font: inherit; }
button, .button {
  border: 1px solid var(--ink);
  border-radius: 999px;
  background: var(--ink);
  color: white;
  padding: .68rem 1.05rem;
  cursor: pointer;
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: .4rem;
}
button.secondary, .button.secondary { color: var(--ink); background: transparent; border-color: var(--line); }
button.accent, .button.accent { background: var(--accent); color: var(--ink); border-color: var(--accent); }
button:focus-visible, a:focus-visible, input:focus-visible, select:focus-visible { outline: 3px solid rgba(251,191,36,.55); outline-offset: 2px; }
.skip-link { position: absolute; left: -9999px; }
.skip-link:focus { left: 1rem; top: 1rem; z-index: 20; background: white; padding: .5rem; }
.site-header { border-bottom: 1px solid rgba(23,23,23,.1); background: rgba(247,245,239,.88); backdrop-filter: blur(18px); position: sticky; top: 0; z-index: 10; }
.nav { max-width: var(--max); margin: auto; min-height: 68px; display: flex; align-items: center; justify-content: space-between; gap: 1rem; padding: .65rem 1.25rem; }
.brand { display: flex; align-items: center; gap: .65rem; text-decoration: none; font-weight: 800; letter-spacing: -.03em; }
.brand-mark { width: 34px; height: 34px; border-radius: 10px; display: grid; place-items: center; background: var(--accent); border: 1px solid rgba(23,23,23,.2); }
.nav-links { display: flex; gap: .2rem; flex-wrap: wrap; }
.nav-links a { text-decoration: none; padding: .4rem .7rem; border-radius: 999px; color: var(--muted); font-size: .9rem; }
.nav-links a[aria-current="page"], .nav-links a:hover { color: var(--ink); background: var(--surface); }
main { max-width: var(--max); margin: auto; padding: 3rem 1.25rem 5rem; min-height: 70vh; }
.hero { display: grid; grid-template-columns: 1.25fr .75fr; gap: 2rem; align-items: end; padding: 2rem 0 3rem; }
.eyebrow { color: var(--muted); text-transform: uppercase; font-size: .78rem; letter-spacing: .16em; font-weight: 800; }
h1 { font-size: clamp(2.7rem, 7vw, 6rem); line-height: .98; letter-spacing: -.07em; margin: .7rem 0 1.2rem; max-width: 900px; }
h2 { font-size: clamp(1.8rem, 4vw, 3rem); line-height: 1.08; letter-spacing: -.045em; margin: 0 0 1rem; }
h3 { line-height: 1.25; letter-spacing: -.02em; }
.lede { font-size: 1.15rem; color: #444; max-width: 720px; }
.hero-actions { display: flex; gap: .7rem; flex-wrap: wrap; margin-top: 1.6rem; }
.proof { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 1.25rem; box-shadow: var(--shadow); }
.proof strong { display: block; font-size: 3rem; line-height: 1; letter-spacing: -.05em; }
.proof p { margin-bottom: 0; color: var(--muted); }
.stats { display: grid; grid-template-columns: repeat(4, 1fr); gap: .8rem; margin: 0 0 3.5rem; }
.stat { border-top: 2px solid var(--ink); padding-top: .75rem; }
.stat strong { display: block; font-size: 1.8rem; letter-spacing: -.04em; }
.stat span { color: var(--muted); font-size: .86rem; }
.section { margin-top: 3.5rem; }
.section-head { display: flex; justify-content: space-between; align-items: end; gap: 1rem; margin-bottom: 1.2rem; }
.section-head p { color: var(--muted); max-width: 620px; margin: 0; }
.grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; }
.card { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 1.2rem; transition: transform .2s, box-shadow .2s; }
.card.clickable { cursor: pointer; }
.card.clickable:hover { transform: translateY(-3px); box-shadow: var(--shadow); }
.card h3 { margin: .45rem 0 .55rem; }
.card p { color: var(--muted); margin: .4rem 0; }
.meta { display: flex; gap: .45rem; flex-wrap: wrap; align-items: center; color: var(--muted); font-size: .8rem; }
.chip { display: inline-flex; align-items: center; min-height: 28px; border-radius: 999px; padding: .2rem .6rem; background: #efede5; font-size: .78rem; }
.chip.accent { background: var(--accent-soft); color: #654800; }
.chip.success { background: #e3f4ea; color: var(--success); }
.toolbar { display: grid; grid-template-columns: 1fr 220px auto; gap: .7rem; margin: 1.5rem 0; position: sticky; top: 82px; z-index: 5; background: var(--paper); padding: .6rem 0; }
.control { width: 100%; border: 1px solid var(--line); background: var(--surface); border-radius: 999px; padding: .7rem 1rem; color: var(--ink); }
.result-note { color: var(--muted); margin: .8rem 0 1.1rem; }
.empty { border: 1px dashed var(--line); border-radius: var(--radius); padding: 2rem; color: var(--muted); text-align: center; grid-column: 1/-1; }
.progress-track { height: 10px; background: #e5e1d7; border-radius: 999px; overflow: hidden; }
.progress-bar { height: 100%; width: 0; background: var(--accent); transition: width .35s; }
.learn-shell { display: grid; grid-template-columns: 260px 1fr; gap: 1.5rem; }
.learn-panel { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 1.25rem; }
.flashcard { min-height: 430px; display: flex; flex-direction: column; justify-content: space-between; }
.flashcard .answer[hidden] { display: none; }
.flashcard ol, .flashcard ul { padding-left: 1.2rem; }
.flashcard-actions { display: flex; flex-wrap: wrap; gap: .6rem; margin-top: 1.2rem; }
.source-row { display: grid; grid-template-columns: 110px 1fr auto; gap: 1rem; align-items: start; border-top: 1px solid var(--line); padding: 1rem 0; }
.source-row:first-child { border-top: 0; }
.source-row a { text-underline-offset: 3px; }
.source-title { font-weight: 700; }
.quiz-option { width: 100%; border-radius: 12px; justify-content: flex-start; text-align: left; margin: .45rem 0; background: var(--surface); color: var(--ink); border-color: var(--line); }
.quiz-option.correct { background: #e3f4ea; border-color: var(--success); }
.quiz-option.wrong { background: #fee9e7; border-color: var(--danger); }
dialog { width: min(760px, calc(100% - 2rem)); max-height: 88vh; border: 0; border-radius: 22px; padding: 0; box-shadow: 0 30px 90px rgba(0,0,0,.25); background: var(--surface); color: var(--ink); }
dialog::backdrop { background: rgba(18,18,18,.55); backdrop-filter: blur(5px); }
.dialog-body { padding: 1.5rem; overflow: auto; max-height: 88vh; }
.dialog-close { float: right; }
.detail-section { border-top: 1px solid var(--line); margin-top: 1rem; padding-top: .8rem; }
.detail-section h3 { margin: 0 0 .4rem; font-size: 1rem; }
.toast { position: fixed; right: 1rem; bottom: 1rem; background: var(--ink); color: white; padding: .8rem 1rem; border-radius: 12px; opacity: 0; transform: translateY(12px); pointer-events: none; transition: .25s; z-index: 30; }
.toast.show { opacity: 1; transform: translateY(0); }
.prose { max-width: 820px; }
.prose h2 { margin-top: 2.5rem; font-size: 2rem; }
.prose li { margin: .35rem 0; }
.footer { border-top: 1px solid var(--line); padding: 1.5rem; color: var(--muted); }
.footer-inner { max-width: var(--max); margin: auto; display: flex; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }
@media (max-width: 860px) {
  .hero, .learn-shell { grid-template-columns: 1fr; }
  .stats { grid-template-columns: repeat(2, 1fr); }
  .grid { grid-template-columns: repeat(2, 1fr); }
  .toolbar { grid-template-columns: 1fr 160px; }
  .toolbar button { grid-column: 1/-1; }
  .nav { align-items: flex-start; }
  .nav-links { justify-content: flex-end; }
}
@media (max-width: 580px) {
  main { padding-top: 2rem; }
  .nav { display: block; }
  .nav-links { overflow-x: auto; flex-wrap: nowrap; justify-content: flex-start; margin-top: .55rem; padding-bottom: .15rem; }
  .nav-links a { white-space: nowrap; }
  .grid, .stats { grid-template-columns: 1fr; }
  .toolbar { grid-template-columns: 1fr; top: 112px; }
  .toolbar button { grid-column: auto; }
  .source-row { grid-template-columns: 1fr; gap: .35rem; }
  h1 { font-size: 3.25rem; }
}
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; transition: none !important; animation: none !important; }
}