/* Zenbuzz — REPL / notebook theme. Cool white, emerald accents, monospace meta,
   chapter "index" rows instead of a card grid, REPL-style fact panel. */
:root {
  --ink: #0d1b17;
  --ink-2: #14261f;
  --slate: #33463e;
  --muted: #5f7369;
  --emerald: #10a175;
  --emerald-dk: #0b7c59;
  --lime: #7bc043;
  --amber: #d6952c;
  --rose: #cf5a67;
  --bg: #f5f8f6;
  --panel: #ffffff;
  --line: #dbe6e0;
  --line-2: #c4d4cb;
  --mono: "SFMono-Regular", "JetBrains Mono", Consolas, "Liberation Mono", Menlo, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0; font-family: var(--sans); color: var(--ink); background: var(--bg);
  line-height: 1.65; font-size: 16px;
}
a { color: var(--emerald-dk); text-decoration: none; }
a:hover { color: var(--rose); }
.wrap { max-width: 1080px; margin: 0 auto; padding: 0 20px; }

/* Header — dark terminal bar with traffic-light dots */
.site-header { background: var(--ink); color: #e7f2ec; border-bottom: 3px solid var(--emerald); position: relative; }
.header-inner { display: flex; align-items: center; justify-content: space-between; flex-wrap: wrap; gap: 12px; padding: 14px 0; }
.brand { display: flex; align-items: center; gap: 11px; color: #fff; }
.brand:hover { color: #fff; }
.brand-mark { color: var(--lime); display: inline-flex; }
.brand-text { font-weight: 700; font-size: 22px; display: flex; flex-direction: column; line-height: 1; letter-spacing: -0.01em; }
.brand-sub { font-family: var(--mono); font-size: 11px; font-weight: 400; color: #7fb79c; margin-top: 5px; }
.site-nav { display: flex; flex-wrap: wrap; gap: 2px; }
.nav-link { font-family: var(--mono); color: #b9d6c7; font-size: 12.5px; padding: 6px 9px; border-bottom: 2px solid transparent; }
.nav-link:hover { color: #fff; border-color: var(--emerald); }
.nav-link.is-active { color: #fff; border-color: var(--lime); }

/* Hero */
.hero { padding: 52px 0 26px; }
.hero-kicker, .cat-head .hero-kicker {
  font-family: var(--mono); font-size: 13px; color: var(--emerald); margin: 0 0 12px; letter-spacing: 0.01em;
}
.hero-title { font-size: 42px; line-height: 1.08; margin: 0 0 14px; color: var(--ink); letter-spacing: -0.02em; max-width: 22ch; }
.hero-lede { font-size: 18px; color: var(--slate); max-width: 62ch; margin: 0 0 16px; }
.hero-note { font-size: 14px; color: var(--ink-2); background: #e4f2ea; border-left: 3px solid var(--emerald); padding: 10px 14px; max-width: 62ch; margin: 0; }

/* Chapters / rows (table-of-contents IA) */
.chapters { padding-bottom: 20px; }
.chapter { margin: 34px 0; }
.chapter-head { display: flex; gap: 14px; align-items: flex-start; border-bottom: 1px solid var(--line-2); padding-bottom: 12px; margin-bottom: 4px; }
.chapter-idx { font-family: var(--mono); font-size: 22px; font-weight: 700; color: var(--emerald); line-height: 1.2; }
.chapter-name { margin: 0 0 3px; font-size: 22px; }
.chapter-name a { color: var(--ink); }
.chapter-name a:hover { color: var(--emerald); }
.chapter-blurb { margin: 0; font-size: 14px; color: var(--muted); max-width: 66ch; }
.rows { list-style: none; margin: 0; padding: 0; }
.rows-wide { margin-bottom: 56px; padding-top: 8px; }
.row { display: flex; align-items: flex-start; gap: 16px; padding: 14px 4px; border-bottom: 1px dashed var(--line); }
.row:hover { background: #eef5f1; }
.row-num { font-family: var(--mono); font-size: 13px; color: var(--muted); padding-top: 3px; min-width: 26px; }
.row-main { flex: 1 1 auto; min-width: 0; }
.row-title { font-size: 18px; font-weight: 600; color: var(--ink); }
.row-title:hover { color: var(--emerald); }
.row-desc { margin: 2px 0 0; font-size: 14px; color: var(--muted); }
.row-tags { display: flex; flex-wrap: wrap; gap: 6px; padding-top: 2px; justify-content: flex-end; }
.pill { font-family: var(--mono); font-size: 11px; padding: 3px 8px; border-radius: 999px; border: 1px solid var(--line-2); color: var(--slate); background: var(--panel); }
.pill-beginner { color: var(--emerald-dk); border-color: #b6e0cd; background: #eaf7f1; }
.pill-intermediate { color: #8a6410; border-color: #ecd9ad; background: #fbf3e0; }
.tag { font-family: var(--mono); font-size: 11px; padding: 3px 8px; border-radius: 999px; background: var(--ink); color: #cfe9dd; }

/* Category head */
.cat-head { padding: 26px 0 18px; }
.cat-title { font-size: 34px; color: var(--ink); margin: 6px 0 10px; letter-spacing: -0.01em; }
.cat-blurb { font-size: 17px; color: var(--slate); max-width: 62ch; margin: 0; }
.crumb { font-family: var(--mono); font-size: 12px; color: var(--muted); padding-top: 22px; }
.crumb a { color: var(--slate); }
.crumb a:hover { color: var(--emerald); }
.crumb .sep { margin: 0 7px; color: var(--line-2); }

/* Concept page */
.concept { max-width: 780px; margin: 0 auto; padding-bottom: 56px; }
.concept-head { padding: 18px 0 6px; }
.concept-title { font-size: 36px; line-height: 1.13; color: var(--ink); margin: 4px 0 6px; letter-spacing: -0.02em; }
.concept-zh { font-family: var(--mono); font-size: 14px; color: var(--muted); margin: 0; }

/* Facts — REPL-ish panel */
.facts { background: var(--ink); border-radius: 8px; padding: 16px 18px; margin: 22px 0 8px; box-shadow: 0 10px 24px -18px rgba(13,27,23,.7); }
.facts-label { font-family: var(--mono); font-size: 12px; color: var(--lime); margin: 0 0 10px; }
.facts-body { display: grid; gap: 6px; }
.fact-line { font-family: var(--mono); font-size: 13.5px; display: flex; gap: 8px; align-items: baseline; }
.fact-key { color: #7fb79c; min-width: 58px; }
.fact-eq { color: #4c6b5c; }
.fact-val { color: #eafff4; word-break: break-word; }

/* Sections */
.sec { margin: 26px 0; padding: 0 0 0 20px; border-left: 3px solid var(--line-2); }
.sec-heading { font-size: 20px; color: var(--ink); margin: 0 0 10px; }
.sec-num { font-family: var(--mono); color: var(--emerald); font-size: 15px; }
.sec-body p { margin: 0 0 14px; }
.sec-body p:last-child { margin-bottom: 0; }

/* Related */
.related { margin: 34px 0 40px; border-top: 1px solid var(--line-2); padding-top: 20px; }
.related-title { font-family: var(--mono); font-size: 13px; text-transform: uppercase; letter-spacing: 0.12em; color: var(--slate); margin: 0 0 12px; }
.rel-rows { display: grid; gap: 8px; }
.rel-row { display: flex; justify-content: space-between; align-items: baseline; gap: 12px; padding: 11px 14px; background: var(--panel); border: 1px solid var(--line); border-left: 3px solid var(--emerald); }
.rel-row:hover { border-left-color: var(--rose); }
.rel-title { font-weight: 600; color: var(--ink); font-size: 15px; }
.rel-meta { font-family: var(--mono); font-size: 11.5px; color: var(--muted); }
.rel-row.is-drip { border-left-color: var(--line-2); opacity: 0.6; }

/* Legal */
.legal { max-width: 760px; margin: 0 auto; padding: 40px 0 56px; }
.legal-title { font-size: 32px; color: var(--ink); margin: 0 0 18px; }
.legal-body h2 { font-size: 20px; color: var(--ink); margin: 24px 0 8px; }
.legal-body p { margin: 0 0 14px; }
.legal-body a { word-break: break-all; }

/* 404 */
.nf { padding: 64px 0 80px; }
.nf-title { font-family: var(--mono); font-size: 30px; color: var(--rose); margin: 0 0 12px; }
.nf-body { color: var(--muted); margin: 0 0 22px; max-width: 54ch; }
.nf-link { display: inline-block; font-family: var(--mono); font-size: 14px; padding: 10px 18px; background: var(--ink); color: #fff; border-radius: 6px; }
.nf-link:hover { background: var(--emerald-dk); color: #fff; }

/* Footer */
.site-footer { background: var(--ink-2); color: #b9d6c7; margin-top: 24px; border-top: 3px solid var(--emerald); }
.site-footer .wrap { padding-top: 24px; padding-bottom: 24px; }
.foot-brand { font-weight: 700; color: #fff; margin: 0 0 8px; }
.foot-links { margin: 0 0 10px; font-size: 14px; font-family: var(--mono); }
.foot-links a { color: #8fc4aa; }
.foot-links a:hover { color: #fff; }
.foot-note { margin: 0; font-size: 13px; color: #86a898; max-width: 68ch; }

@media (max-width: 640px) {
  .hero-title { font-size: 30px; }
  .concept-title, .cat-title { font-size: 26px; }
  .header-inner { flex-direction: column; align-items: flex-start; }
  .row { flex-wrap: wrap; }
  .row-tags { justify-content: flex-start; }
  .fact-key { min-width: 52px; }
}