:root {
  --ink: #1a1814;
  --ink-soft: #3d3830;
  --paper: #f4efe4;
  --paper-2: #ebe4d4;
  --rule: #d4cbb8;
  --forest: #14352c;
  --forest-2: #1e4d40;
  --gold: #b08948;
  --gold-2: #c9a227;
  --rust: #8c3b2a;
  --code-bg: #121a18;
  --code-fg: #e8efe9;
  --ok: #2d6a4f;
  --io-in: #1e3a5f;
  --io-out: #1b4332;
  --shadow: 0 18px 50px rgba(20, 53, 44, 0.12);
  --serif: "Source Serif 4", "Times New Roman", serif;
  --sans: "Outfit", "Segoe UI", sans-serif;
  --mono: "IBM Plex Mono", "Consolas", monospace;
}

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--sans);
  background: var(--paper);
  color: var(--ink);
  min-height: 100vh;
}

.bg-grain {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  background-image:
    radial-gradient(ellipse at 12% 8%, rgba(176, 137, 72, 0.08), transparent 42%),
    radial-gradient(ellipse at 90% 100%, rgba(20, 53, 44, 0.08), transparent 46%);
}

.app { display: grid; grid-template-columns: 280px 1fr; min-height: 100vh; position: relative; z-index: 1; }

.sidebar {
  background: var(--forest);
  color: #e8efe9;
  padding: 28px 18px 40px;
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
  border-right: 4px solid var(--gold);
}
.brand { display: flex; gap: 12px; align-items: center; margin-bottom: 22px; }
.crest {
  width: 48px; height: 48px;
  border: 2px solid var(--gold);
  display: grid; place-items: center;
  font-family: var(--serif);
  font-weight: 700;
  color: var(--gold-2);
  letter-spacing: 0.04em;
}
.brand h1 { font-size: 13px; font-weight: 600; line-height: 1.25; letter-spacing: 0.08em; text-transform: uppercase; }
.brand p { font-size: 11px; opacity: 0.7; margin-top: 2px; }

.search {
  width: 100%;
  background: #0e241e;
  border: 1px solid #2c5a4c;
  color: #e8efe9;
  padding: 10px 12px;
  font-family: var(--sans);
  font-size: 13px;
  margin-bottom: 18px;
}
.search:focus { outline: 1px solid var(--gold); }

.nav-sec { margin-bottom: 16px; }
.nav-sec h2 {
  font-size: 10px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--gold);
  margin-bottom: 8px;
  font-weight: 600;
}
.nav-sec a, .nav-sec button {
  display: block;
  width: 100%;
  text-align: left;
  background: transparent;
  border: 0;
  color: #d5e4dc;
  padding: 6px 8px;
  font-size: 12.5px;
  font-family: var(--sans);
  cursor: pointer;
  text-decoration: none;
  border-left: 2px solid transparent;
}
.nav-sec a:hover, .nav-sec button:hover, .nav-sec a.active, .nav-sec button.active {
  border-left-color: var(--gold);
  color: #fff;
  background: rgba(201, 162, 39, 0.08);
}

.main { padding: 0 0 80px; min-width: 0; }
.topbar {
  background: linear-gradient(180deg, #fffdf8 0%, var(--paper) 100%);
  border-bottom: 1px solid var(--rule);
  padding: 18px 36px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: sticky;
  top: 0;
  z-index: 5;
}
.topbar .meta { font-size: 12px; color: var(--ink-soft); letter-spacing: 0.06em; text-transform: uppercase; }
.topbar .actions { display: flex; gap: 8px; }
.btn {
  border: 1px solid var(--forest);
  background: var(--forest);
  color: #fff;
  font-family: var(--sans);
  font-size: 12px;
  padding: 8px 12px;
  cursor: pointer;
  letter-spacing: 0.04em;
}
.btn.ghost { background: transparent; color: var(--forest); }
.btn:hover { background: var(--forest-2); color: #fff; }

.cover, .sheet { padding: 36px 48px; max-width: 1080px; }

.cover-card {
  background: #fffdf8;
  border: 1px solid var(--rule);
  box-shadow: var(--shadow);
  padding: 48px 52px 56px;
  position: relative;
}
.cover-card::before {
  content: "";
  position: absolute;
  left: 0; top: 0; bottom: 0;
  width: 10px;
  background: linear-gradient(180deg, var(--gold) 0%, var(--forest) 100%);
}
.kicker {
  font-size: 11px;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--gold);
  font-weight: 600;
}
.cover-card h2 {
  font-family: var(--serif);
  font-size: 42px;
  font-weight: 600;
  line-height: 1.15;
  margin: 10px 0 8px;
  color: var(--forest);
}
.cover-card .sub {
  font-family: var(--serif);
  font-style: italic;
  font-size: 18px;
  color: var(--ink-soft);
  margin-bottom: 28px;
}
.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 14px 32px; }
.field label { display: block; font-size: 11px; letter-spacing: 0.08em; text-transform: uppercase; color: var(--ink-soft); }
.field .line {
  border-bottom: 1px solid #cbbfa6;
  min-height: 28px;
  font-size: 15px;
  padding-top: 4px;
}
.stamp {
  margin-top: 32px;
  border: 2px dashed var(--gold);
  padding: 16px 18px;
  font-size: 13px;
  color: var(--ink-soft);
  line-height: 1.55;
}

.section-head {
  margin: 8px 0 22px;
}
.section-head h2 {
  font-family: var(--serif);
  font-size: 30px;
  color: var(--forest);
}
.section-head p { color: var(--ink-soft); margin-top: 6px; max-width: 68ch; }

.exp {
  background: #fffdf8;
  border: 1px solid var(--rule);
  margin-bottom: 28px;
  box-shadow: 0 8px 24px rgba(26, 24, 20, 0.05);
  break-inside: avoid;
}
.exp-head {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  align-items: baseline;
  padding: 16px 22px;
  border-bottom: 1px solid var(--rule);
  background: linear-gradient(90deg, #f7f1e4, #fffdf8);
}
.exp-no {
  font-size: 11px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--rust);
  font-weight: 700;
}
.exp-head h3 {
  font-family: var(--serif);
  font-size: 20px;
  color: var(--forest);
  margin-top: 4px;
}
.exp-body { padding: 18px 22px 22px; }
.aim, .algo, .result {
  font-size: 14.5px;
  line-height: 1.65;
  margin-bottom: 14px;
}
.aim strong, .algo strong, .result strong { color: var(--forest); }
.algo ol { margin: 6px 0 0 18px; }
.algo li { margin: 2px 0; }

.code-wrap { position: relative; margin: 12px 0 16px; }
.code-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: #0c1614;
  color: #c9d6cf;
  padding: 8px 12px;
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}
.code-bar .btns { display: flex; gap: 6px; }
.code-bar button {
  background: transparent;
  border: 1px solid #3a524a;
  color: #e8efe9;
  font-size: 11px;
  padding: 4px 8px;
  cursor: pointer;
  font-family: var(--sans);
}
pre {
  background: var(--code-bg);
  color: var(--code-fg);
  padding: 16px 18px 20px;
  overflow-x: auto;
  font-family: var(--mono);
  font-size: 12.5px;
  line-height: 1.55;
}
.kw { color: #7dd3b0; }
.str { color: #e7c27d; }
.cm { color: #6f847c; font-style: italic; }
.num { color: #f0a07a; }
.fn { color: #9ecbff; }
.pp { color: #c9a0ff; }

.io {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-bottom: 12px;
}
.io-box { border: 1px solid var(--rule); }
.io-box h4 {
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  padding: 8px 12px;
  color: #fff;
}
.io-box.in h4 { background: var(--io-in); }
.io-box.out h4 { background: var(--io-out); }
.io-box pre {
  background: #faf7f0;
  color: var(--ink);
  min-height: 72px;
  white-space: pre-wrap;
}
.result {
  background: #eef6f1;
  border-left: 4px solid var(--ok);
  padding: 10px 14px;
}

.hidden { display: none !important; }
.toc {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 8px 24px;
  margin-top: 18px;
}
.toc a {
  color: var(--forest);
  text-decoration: none;
  font-size: 14px;
  border-bottom: 1px dotted var(--rule);
  padding: 6px 0;
  display: flex;
  justify-content: space-between;
  gap: 12px;
}
.toc a:hover { color: var(--rust); }
.toc span { color: var(--ink-soft); font-variant-numeric: tabular-nums; }

.menu-btn { display: none; }

@media (max-width: 980px) {
  .app { grid-template-columns: 1fr; }
  .sidebar { position: fixed; left: -300px; z-index: 20; transition: left 0.2s; }
  .sidebar.open { left: 0; }
  .menu-btn { display: inline-block; }
  .cover, .sheet { padding: 20px 16px; }
  .cover-card { padding: 24px 20px; }
  .cover-card h2 { font-size: 30px; }
  .grid-2, .io, .toc { grid-template-columns: 1fr; }
}

@media print {
  .sidebar, .topbar, .code-bar button, .bg-grain { display: none !important; }
  .app { display: block; }
  .exp { break-inside: avoid; box-shadow: none; }
  pre { white-space: pre-wrap; }
  body { background: #fff; }
}