:root {
  --bg: #ffffff;
  --fg: #0a0a0a;
  --muted: #6b6b6b;
  --line: #e6e6e6;
  --elev: #f7f7f7;
  --shadow: 0 10px 30px rgba(0,0,0,0.06);
  --radius: 14px;
  --speed: 180ms;
}
:root.dark {
  --bg: #0c0c0c;
  --fg: #f5f5f5;
  --muted: #b5b5b5;
  --line: #1d1d1d;
  --elev: #101010;
  --shadow: 0 10px 30px rgba(0,0,0,0.3);
}
* { box-sizing: border-box; }
html, body { height: 100%; scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: 'Noto Sans', system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
  background: var(--bg); color: var(--fg);
  line-height: 1.6;
}
.site-header {
  position: sticky; top: 0; z-index: 50;
  display: grid; grid-template-columns: 1fr auto auto;
  gap: 1rem; align-items: center;
  padding: 0.75rem 1rem; border-bottom: 1px solid var(--line);
  background: color-mix(in oklab, var(--bg) 92%, transparent);
  backdrop-filter: saturate(140%) blur(8px);
}
.brand { font-weight: 700; text-decoration: none; color: var(--fg); }
.nav-toggle { display: none; }
.nav-list { display: flex; gap: 1rem; list-style: none; margin: 0; padding: 0; }
.nav-list a { color: var(--fg); text-decoration: none; padding: .4rem .6rem; border-radius: 8px; }
.nav-list a.active, .nav-list a:hover { background: var(--elev); }
.tools { display: flex; gap: 0.75rem; align-items: center; }
.icon-btn {
  background: var(--elev); border: 1px solid var(--line);
  padding: .5rem .6rem; border-radius: 10px; cursor: pointer; color: var(--fg);
}
.search { position: relative; }
.search input {
  width: 240px; max-width: 52vw; padding: .55rem .7rem;
  border: 1px solid var(--line); border-radius: 10px; background: var(--bg); color: var(--fg);
}
.search-results {
  position: absolute; inset-inline: 0; top: calc(100% + 6px);
  background: var(--bg); border: 1px solid var(--line); border-radius: 12px;
  box-shadow: var(--shadow); display: none; max-height: 50vh; overflow: auto;
}
.search-results.show { display: block; }
.search-results a { display: block; padding: .6rem .75rem; color: var(--fg); text-decoration: none; border-bottom: 1px solid var(--line); }
.search-results a:last-child { border-bottom: 0; }
.search-results em { color: var(--muted); font-style: normal; }

.hero { padding: 9vh 1rem 8vh; border-bottom: 1px solid var(--line); }
.hero-inner { max-width: 1100px; margin: 0 auto; text-align: center; }
h1 { font-size: clamp(2rem, 4.8vw, 4rem); line-height: 1.1; margin: 0 0 .5rem; }
.subtitle { color: var(--muted); margin: 0 auto 1rem; max-width: 820px; }
.hero-cta { display: flex; gap: .75rem; justify-content: center; margin-top: 1rem; }
.btn { background: var(--fg); color: var(--bg); border: 1px solid var(--fg); padding: .7rem 1rem; border-radius: 12px; text-decoration: none; }
.btn.ghost { background: transparent; color: var(--fg); }

.section { padding: 5rem 1rem; }
.section.alt { background: var(--elev); }
.container { max-width: 1100px; margin: 0 auto; }
.section h2 { font-size: clamp(1.4rem, 2.4vw, 2rem); margin-top: 0; }

.key-points { display: grid; gap: .4rem; padding-left: 1rem; }
.grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 1rem; }
.card {
  border: 1px solid var(--line); border-radius: var(--radius);
  padding: 1rem; background: var(--bg); box-shadow: var(--shadow);
  transition: transform var(--speed) ease, box-shadow var(--speed) ease;
}
.card:hover { transform: translateY(-2px); }

.accordion details {
  border: 1px solid var(--line); border-radius: 12px; background: var(--bg); margin-bottom: .75rem;
}
.accordion summary {
  cursor: pointer; padding: .9rem 1rem; font-weight: 600; list-style: none;
}
.accordion .details-body { border-top: 1px solid var(--line); padding: .9rem 1rem; }
.code {
  background: var(--elev); border: 1px solid var(--line); border-radius: 10px;
  padding: .75rem; overflow: auto;
}

.glossary-controls { margin-bottom: .75rem; }
.glossary { display: grid; grid-template-columns: repeat(2, 1fr); gap: .75rem 1.25rem; }
.glossary dt { font-weight: 700; }
.glossary dd { margin: 0 0 .5rem 0; color: var(--muted); }

.quiz { display: grid; gap: 1rem; }
.quiz .q {
  border: 1px solid var(--line); border-radius: 12px; padding: 1rem; background: var(--bg);
}
.quiz .q legend { font-weight: 700; margin-bottom: .5rem; }
.quiz .options { display: grid; gap: .25rem; }
.quiz .submit-row { display: flex; gap: .75rem; align-items: center; }
.quiz-score { margin-top: .75rem; font-weight: 700; }
.correct { outline: 2px solid #2ecc71; }
.incorrect { outline: 2px solid #e74c3c; }

.site-footer { border-top: 1px solid var(--line); padding: 2rem 1rem; color: var(--muted); }
.footer-grid { display: grid; grid-template-columns: 2fr 1fr 1fr; gap: 1rem; align-items: start; }
.footer-nav { list-style: none; padding: 0; margin: 0; display: grid; gap: .25rem; }
.footer-nav a { color: var(--fg); text-decoration: none; }

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

@media (max-width: 960px) {
  .grid { grid-template-columns: repeat(2, 1fr); }
  .glossary { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
}
@media (max-width: 680px) {
  .site-header { grid-template-columns: 1fr auto; grid-template-areas: "brand tools" "nav nav"; row-gap: .5rem; }
  .brand { grid-area: brand; }
  .tools { grid-area: tools; }
  .nav { grid-area: nav; }
  .nav-toggle { display: inline-flex; align-items: center; padding: .45rem .6rem; border: 1px solid var(--line); background: var(--bg); border-radius: 10px; }
  .nav-list { display: none; flex-direction: column; border: 1px solid var(--line); border-radius: 12px; padding: .5rem; background: var(--bg); }
  .nav-list.show { display: flex; }
}