:root {
  --bg: #f5f7f6;
  --surface: #ffffff;
  --ink: #15212b;
  --muted: #5d6974;
  --line: #e2e6e9;
  --brand: #0d8a6a;
  --brand-ink: #066049;
  --brand-soft: #e3f4ee;
  --accent: #f2a516;
  --accent-soft: #fff6e0;
  --bad: #c5302b;
  --bad-soft: #fdecea;
  --info-soft: #eef3fb;
  --grid-head: #f1f3f4;
  --grid-line: #e1e3e6;
  --radius: 12px;
  --shadow: 0 1px 2px rgba(16, 24, 40, .05), 0 4px 16px rgba(16, 24, 40, .06);
  --mono: 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --sans: 'Inter', system-ui, -apple-system, 'Segoe UI', Roboto, sans-serif;
  --top: 60px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 15px/1.6 var(--sans); -webkit-font-smoothing: antialiased; }
a { color: var(--brand-ink); }
code, kbd, pre { font-family: var(--mono); }
code { background: #eef1f3; padding: 1px 6px; border-radius: 5px; font-size: .88em; }
kbd { border: 1px solid var(--line); border-bottom-width: 2px; border-radius: 5px; padding: 0 5px; font-size: .82em; background: #fff; }

/* ---------- top bar ---------- */
.topbar { position: sticky; top: 0; z-index: 30; height: var(--top); display: flex; align-items: center; gap: 24px; padding: 0 20px; background: rgba(255,255,255,.92); backdrop-filter: blur(8px); border-bottom: 1px solid var(--line); }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; color: var(--ink); font-weight: 600; letter-spacing: -.01em; font-size: 16px; white-space: nowrap; }
.brand b { color: var(--brand); font-weight: 700; }
.brand svg { flex: none; }
.topnav { display: flex; gap: 4px; }
.topnav a { text-decoration: none; color: var(--muted); font-weight: 500; padding: 6px 12px; border-radius: 8px; }
.topnav a:hover { background: var(--bg); color: var(--ink); }
.overall { margin-left: auto; font-size: 13px; color: var(--brand-ink); background: var(--brand-soft); padding: 3px 10px; border-radius: 99px; }
.overall:empty { display: none; }
.menu-btn { display: none; margin-left: auto; border: 1px solid var(--line); background: #fff; border-radius: 8px; padding: 6px 10px; font: inherit; cursor: pointer; }

/* ---------- lesson layout ---------- */
.layout { display: grid; grid-template-columns: 290px minmax(0, 1fr); min-height: calc(100vh - var(--top)); }
.sidebar { position: sticky; top: var(--top); height: calc(100vh - var(--top)); overflow-y: auto; border-right: 1px solid var(--line); background: var(--surface); padding: 14px 10px 40px; }
.side-cat { font-size: 11px; font-weight: 700; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); padding: 16px 12px 6px; }
.side-link { display: flex; align-items: center; gap: 10px; padding: 7px 12px; border-radius: 8px; color: var(--ink); text-decoration: none; font-size: 14px; }
.side-link:hover { background: var(--bg); }
.side-link .n { flex: none; width: 22px; height: 22px; border-radius: 50%; display: grid; place-items: center; font-size: 11px; font-weight: 600; background: var(--bg); color: var(--muted); border: 1px solid var(--line); }
.side-link.current { background: var(--brand-soft); font-weight: 600; }
.side-link.current .n { border-color: var(--brand); color: var(--brand-ink); }
.side-link.started .n { border-color: var(--accent); }
.side-link.done .n { background: var(--brand); border-color: var(--brand); color: transparent; position: relative; }
.side-link.done .n::after { content: '✓'; color: #fff; position: absolute; font-size: 12px; }

.main { padding: 28px 40px 80px; max-width: 1040px; width: 100%; min-width: 0; }
.crumbs { font-size: 13px; color: var(--muted); margin-bottom: 10px; }
.crumbs a { color: var(--muted); text-decoration: none; }
.crumbs a:hover { color: var(--ink); }
.chip { display: inline-block; font-size: 12px; font-weight: 600; color: var(--brand-ink); background: var(--brand-soft); padding: 2px 10px; border-radius: 99px; }
h1 { font-size: 30px; line-height: 1.2; letter-spacing: -.02em; margin: 8px 0 6px; }
.lede { color: var(--muted); margin: 0 0 22px; max-width: 70ch; }

/* ---------- practice card ---------- */
.card { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow); }
.practice { padding: 20px 22px 18px; }
.practice-top { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-bottom: 8px; }
.task-label { font-size: 12px; font-weight: 700; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); }
.steps { display: flex; gap: 6px; }
.step { width: 28px; height: 28px; border-radius: 50%; border: 1.5px solid var(--line); background: #fff; font: 600 12px var(--sans); color: var(--muted); cursor: pointer; }
.step.current { border-color: var(--brand); color: var(--brand-ink); box-shadow: 0 0 0 3px var(--brand-soft); }
.step.done { background: var(--brand); border-color: var(--brand); color: #fff; }
.prompt { font-size: 17px; line-height: 1.55; margin: 4px 0 16px; min-height: 2.4em; }

.sheet { border: 1px solid var(--grid-line); border-radius: 8px; overflow: visible; background: #fff; }
.fbar { display: flex; align-items: stretch; border-bottom: 1px solid var(--grid-line); background: #fff; border-radius: 8px 8px 0 0; position: relative; }
.namebox { flex: none; width: 74px; padding: 7px 10px; font: 500 13px var(--mono); color: var(--ink); border-right: 1px solid var(--grid-line); display: flex; align-items: center; overflow: hidden; white-space: nowrap; }
.fx-label { flex: none; padding: 0 10px; display: flex; align-items: center; font: italic 600 14px Georgia, serif; color: var(--muted); border-right: 1px solid var(--grid-line); }
.fx-wrap { position: relative; flex: 1; min-width: 0; }
#fx, .demo .fx-wrap input { width: 100%; border: 0; outline: 0; padding: 9px 12px; font: 14px var(--mono); color: var(--ink); background: transparent; }
.fx-wrap:focus-within { box-shadow: inset 0 -2px 0 var(--brand); }
.sig, .ac { position: absolute; left: 8px; top: calc(100% + 6px); z-index: 20; background: #fff; border: 1px solid var(--line); border-radius: 8px; box-shadow: 0 8px 24px rgba(16,24,40,.14); }
.sig { padding: 8px 12px; max-width: min(560px, 92vw); font-size: 13px; }
.sig-line { font-family: var(--mono); }
.sig .cur { background: var(--accent-soft); border-bottom: 2px solid var(--accent); font-weight: 600; }
.sig-desc { color: var(--muted); margin-top: 3px; font-size: 12.5px; }
.ac { list-style: none; margin: 0; padding: 4px; min-width: 300px; max-width: 92vw; }
.ac li { display: flex; gap: 10px; align-items: baseline; padding: 5px 9px; border-radius: 6px; cursor: pointer; font-size: 13px; }
.ac li b { font-family: var(--mono); font-weight: 600; }
.ac li span { color: var(--muted); font-size: 12px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.ac li.on, .ac li:hover { background: var(--brand-soft); }

.grid-scroll { overflow-x: auto; border-radius: 0 0 8px 8px; }
.grid { border-collapse: collapse; font-size: 13px; user-select: none; min-width: 100%; }
.grid th { background: var(--grid-head); color: #5f6368; font-weight: 500; font-size: 12px; border: 1px solid var(--grid-line); padding: 3px 6px; text-align: center; }
.grid thead th { height: 24px; }
.grid tbody th { width: 42px; min-width: 42px; }
.grid th.corner { width: 42px; }
.grid th.active { background: #dfe6ec; color: var(--ink); font-weight: 600; }
.grid td { border: 1px solid var(--grid-line); height: 27px; min-width: 104px; max-width: 220px; padding: 0 7px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; cursor: cell; background: #fff; }
.grid td.num { text-align: right; }
.grid td.bool { text-align: center; }
.grid td.header { font-weight: 600; background: #fafbfb; }
.grid td.label { font-weight: 600; color: var(--brand-ink); }
.grid td.input { background: #f3f7ff; font-weight: 500; }
.grid td.selected { outline: 2px solid var(--brand); outline-offset: -2px; }
.grid td.target { background: var(--accent-soft); outline: 2px dashed var(--accent); outline-offset: -2px; }
.grid td.target.selected { outline-style: solid; }
.grid td.target:empty::after { content: '?'; color: #c08a1a; font-weight: 700; display: block; text-align: center; }
.grid td.preview { color: #3c4650; }
.grid td.err { color: var(--bad); font-weight: 600; }
.grid td.correct { background: var(--brand-soft); outline: 2px solid var(--brand); color: var(--brand-ink); font-weight: 600; }

.actions { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 16px; }
.btn { appearance: none; border: 1px solid var(--line); background: #fff; color: var(--ink); font: 500 14px var(--sans); padding: 8px 14px; border-radius: 8px; cursor: pointer; text-decoration: none; display: inline-flex; align-items: center; gap: 6px; }
.btn:hover { border-color: #c9d0d6; background: #fafbfb; }
.btn.primary { background: var(--brand); border-color: var(--brand); color: #fff; }
.btn.primary:hover { background: var(--brand-ink); }
.btn.ghost { border-color: transparent; color: var(--muted); }
.actions .spacer { flex: 1; }

.feedback { margin-top: 14px; border-radius: 8px; font-size: 14.5px; }
.feedback:empty { display: none; }
.feedback.good, .feedback.bad, .feedback.info { padding: 12px 14px; display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 10px; }
.feedback.good { background: var(--brand-soft); border: 1px solid #b7e2d3; }
.feedback.bad { background: var(--bad-soft); border: 1px solid #f5c2bf; }
.feedback.info { background: var(--info-soft); border: 1px solid #d3def0; }
.feedback .fb-actions { display: flex; gap: 8px; }
.complete-badge { display: inline-block; margin-left: 6px; font-weight: 600; color: var(--brand-ink); }
.shake { animation: shake .35s; }
@keyframes shake { 20%, 60% { transform: translateX(-4px); } 40%, 80% { transform: translateX(4px); } }
.kbd-tip { color: var(--muted); font-size: 12.5px; margin: 12px 0 0; }

/* ---------- learn article ---------- */
.learn { margin-top: 36px; max-width: 760px; }
.learn h2 { font-size: 22px; letter-spacing: -.01em; margin: 0 0 10px; }
.learn h3 { font-size: 17px; margin: 24px 0 8px; }
.learn p, .learn li { color: #2b3640; }
.learn pre.syntax { background: #10201b; color: #d8f3e8; padding: 14px 16px; border-radius: 10px; overflow-x: auto; font-size: 13.5px; line-height: 1.7; }
.ref-table { border-collapse: collapse; margin: 12px 0; font-size: 14px; }
.ref-table th, .ref-table td { border: 1px solid var(--line); padding: 6px 12px; text-align: left; }
.ref-table th { background: var(--grid-head); font-weight: 600; }
.pager { display: flex; justify-content: space-between; gap: 12px; margin-top: 40px; padding-top: 20px; border-top: 1px solid var(--line); }
.pager a { text-decoration: none; display: flex; flex-direction: column; padding: 10px 14px; border: 1px solid var(--line); border-radius: 10px; background: #fff; max-width: 48%; }
.pager a small { color: var(--muted); font-size: 12px; }
.pager a.next { margin-left: auto; text-align: right; }

/* ---------- home ---------- */
.home main { max-width: 1120px; margin: 0 auto; padding: 0 24px 80px; }
.hero { display: grid; grid-template-columns: 1.05fr .95fr; gap: 48px; align-items: center; padding: 64px 0 40px; }
.hero h1 { font-size: 46px; line-height: 1.08; letter-spacing: -.03em; margin: 14px 0 16px; }
.hero h1 em { font-style: normal; color: var(--brand); }
.hero p { font-size: 18px; color: var(--muted); margin: 0 0 26px; max-width: 46ch; }
.hero .cta { display: flex; gap: 10px; flex-wrap: wrap; }
.hero .btn { padding: 11px 18px; font-size: 15px; }
.demo { padding: 0; overflow: hidden; transform: rotate(-1deg); }
.demo .fbar { border-radius: 0; }
.demo .grid { table-layout: fixed; width: 100%; }
.demo .grid td { min-width: 0; cursor: default; }
.demo .grid th.corner, .demo .grid tbody th { width: 34px; min-width: 34px; }
.demo-note { padding: 10px 14px; font-size: 13px; background: var(--brand-soft); color: var(--brand-ink); border-top: 1px solid #c6e8dc; font-weight: 500; }
.stats { display: flex; flex-wrap: wrap; gap: 10px 28px; color: var(--muted); font-size: 14px; padding: 6px 0 40px; border-bottom: 1px solid var(--line); }
.stats b { color: var(--ink); font-size: 18px; margin-right: 4px; }
.section-title { font-size: 26px; letter-spacing: -.02em; margin: 52px 0 6px; }
.section-sub { color: var(--muted); margin: 0 0 22px; }
.how { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }
.how .card { padding: 20px; }
.how .k { width: 30px; height: 30px; border-radius: 8px; display: grid; place-items: center; background: var(--brand-soft); color: var(--brand-ink); font-weight: 700; margin-bottom: 10px; }
.how h3 { margin: 0 0 4px; font-size: 16px; }
.how p { margin: 0; color: var(--muted); font-size: 14px; }
.cat-block { margin-top: 30px; }
.cat-block h3 { font-size: 13px; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin: 0 0 10px; }
.lesson-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 12px; }
.lesson-card { position: relative; display: block; padding: 14px 16px; text-decoration: none; color: var(--ink); transition: border-color .15s, transform .15s; }
.lesson-card:hover { border-color: var(--brand); transform: translateY(-1px); }
.lesson-card .t { font-weight: 600; }
.lesson-card .m { font-size: 12.5px; color: var(--muted); margin-top: 2px; }
.lesson-card .fns { font: 11.5px var(--mono); color: var(--brand-ink); margin-top: 8px; }
.lesson-card.done::after { content: '✓ Done'; position: absolute; top: 12px; right: 12px; font-size: 11px; font-weight: 700; color: #fff; background: var(--brand); padding: 1px 8px; border-radius: 99px; }
.lesson-card.started::after { content: 'In progress'; position: absolute; top: 12px; right: 12px; font-size: 11px; font-weight: 700; color: #8a5a00; background: var(--accent-soft); padding: 1px 8px; border-radius: 99px; }
.faq details { background: #fff; border: 1px solid var(--line); border-radius: 10px; padding: 12px 16px; margin-bottom: 8px; }
.faq summary { cursor: pointer; font-weight: 600; }
.faq p { color: var(--muted); margin: 8px 0 0; }

/* ---------- cheat sheet ---------- */
.page { max-width: 1040px; margin: 0 auto; padding: 32px 24px 80px; }
.cheat { width: 100%; border-collapse: collapse; background: #fff; border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; margin-bottom: 28px; font-size: 14px; }
.cheat th, .cheat td { padding: 9px 14px; border-bottom: 1px solid var(--line); text-align: left; vertical-align: top; }
.cheat th { background: var(--grid-head); font-size: 12px; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); }
.cheat td:first-child { font: 600 13px var(--mono); white-space: nowrap; }
.cheat td.syn { font: 12.5px var(--mono); color: #33414d; }
.cheat a { white-space: nowrap; }

/* ---------- function pages ---------- */
.fn-ref { margin-top: 22px; }
.fn-ref h2 { margin-top: 34px; }
.fn-ref > h2:first-child { margin-top: 0; }
.args { display: grid; grid-template-columns: max-content 1fr; gap: 8px 16px; margin: 14px 0 0; }
.args dt { margin: 0; }
.args dd { margin: 0; color: #2b3640; }
.practice-title { font-size: 22px; letter-spacing: -.01em; margin: 34px 0 12px; }
.sample { margin: 14px 0 18px; }
.sample figcaption { font-size: 12.5px; color: var(--muted); margin-top: 6px; }
.grid.static td { cursor: default; min-width: 0; }
.grid.static { min-width: 0; }
.table-scroll { overflow-x: auto; }
.examples { width: 100%; }
.examples td:first-child { white-space: nowrap; }
.examples td.res { font-weight: 600; white-space: nowrap; color: var(--brand-ink); }
.examples td.res.err { color: var(--bad); }
.related { display: grid; grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); gap: 10px; }
.rel-card { display: flex; flex-direction: column; gap: 2px; padding: 12px 14px; text-decoration: none; color: var(--ink); }
.rel-card b { font-family: var(--mono); color: var(--brand-ink); }
.rel-card span { font-size: 13px; color: var(--muted); }
.rel-card:hover { border-color: var(--brand); }
.course-link { margin-top: 26px; padding: 12px 16px; background: var(--brand-soft); border-radius: 10px; }
.guide-links { margin-top: 26px; padding: 12px 16px; border: 1px solid var(--line); background: #fff; border-radius: 10px; display: flex; flex-wrap: wrap; gap: 6px 16px; align-items: center; }
.side-link.fn-link { font-family: var(--mono); font-size: 13px; padding: 5px 12px; }
.side-link.side-hub { font-weight: 600; color: var(--brand-ink); }
.fn-index { display: grid; gap: 18px; }
.fn-group h3 { font-size: 13px; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin: 0 0 8px; }
.fn-chips { display: flex; flex-wrap: wrap; gap: 6px; }
.fn-chips a { font: 500 13px var(--mono); text-decoration: none; color: var(--ink); background: #fff; border: 1px solid var(--line); border-radius: 7px; padding: 5px 10px; }
.fn-chips a:hover { border-color: var(--brand); color: var(--brand-ink); }
.cheat-toc { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 4px; }
.cheat-toc a { text-decoration: none; font-size: 13px; font-weight: 600; padding: 4px 12px; border-radius: 99px; background: var(--brand-soft); }
.cheat td:first-child a { color: var(--brand-ink); text-decoration: none; }
.foot-links { display: flex; flex-wrap: wrap; justify-content: center; gap: 4px 14px; margin-bottom: 10px; }
.foot-links a { color: var(--muted); font: 12.5px var(--mono); }

.home-copy { max-width: 760px; }
.home-copy p, .home-copy li { color: #2b3640; font-size: 16px; }
.home-copy h3 { font-size: 17px; margin: 22px 0 6px; }
.home-copy .learn-list li { margin-bottom: 6px; }

footer.site { border-top: 1px solid var(--line); padding: 22px 24px; color: var(--muted); font-size: 13px; text-align: center; background: var(--surface); }

/* ---------- responsive ---------- */
@media (max-width: 960px) {
  .layout { grid-template-columns: minmax(0, 1fr); }
  .sidebar { display: none; position: fixed; inset: var(--top) 0 0 0; height: auto; z-index: 25; border-right: 0; }
  .nav-open .sidebar { display: block; }
  .menu-btn { display: inline-block; }
  .overall { display: none; }
  .main { padding: 20px 16px 60px; }
  .hero { grid-template-columns: 1fr; padding-top: 36px; gap: 28px; }
  .hero h1 { font-size: 36px; }
  .how { grid-template-columns: 1fr; }
}
@media (max-width: 600px) {
  .args { grid-template-columns: 1fr; gap: 2px; }
  .args dd { margin-bottom: 10px; }
  .topnav { display: none; }
  .practice { padding: 16px 14px; }
  .prompt { font-size: 16px; }
  .namebox { width: 56px; }
  h1 { font-size: 25px; }
  .home main, .page { padding-left: 16px; padding-right: 16px; }
  .pager a { max-width: 100%; }
}