:root {
  --bg: #f6f1e7;
  --paper: #fffaf1;
  --ink: #1c1915;
  --muted: #6b645b;
  --line: rgba(28, 25, 21, 0.12);
  --accent: #8a3b12;
  --max: 38rem;
  --font-serif: "Source Serif 4", "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif;
  --font-sans: "Source Sans 3", ui-sans-serif, system-ui, sans-serif;
  --font-system: ui-sans-serif, system-ui, -apple-system, "Segoe UI", sans-serif;
  --font: var(--font-serif);
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #161412;
    --paper: #1d1a17;
    --ink: #f3ece2;
    --muted: #b3aaa0;
    --line: rgba(243, 236, 226, 0.14);
    --accent: #e8a27a;
    color-scheme: dark;
  }
}

* { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font);
  font-size: 1.18rem;
  line-height: 1.7;
  font-optical-sizing: auto;
}

html[data-font="serif"] { --font: var(--font-serif); }
html[data-font="sans"] { --font: var(--font-sans); }
html[data-font="system"] { --font: var(--font-system); }
html[data-font="sans"] body,
html[data-font="system"] body {
  font-size: 1.12rem;
  line-height: 1.65;
  letter-spacing: 0.005em;
}

.skip {
  position: absolute;
  left: -999px;
}

.top {
  position: sticky;
  top: 0;
  z-index: 5;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  padding: 0.85rem 1.1rem;
  padding-top: calc(0.85rem + env(safe-area-inset-top));
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--line);
}

.mark {
  color: inherit;
  text-decoration: none;
  font-family: var(--font-sans);
  font-size: 0.82rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.top-actions {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.font-switch {
  display: flex;
  border: 1px solid var(--line);
  background: var(--paper);
  border-radius: 999px;
  overflow: hidden;
}

.font-switch button {
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--muted);
  padding: 0.42rem 0.62rem;
  font: inherit;
  font-family: var(--font-sans);
  font-size: 0.78rem;
}

.font-switch button[aria-pressed="true"] {
  background: color-mix(in srgb, var(--ink) 8%, var(--paper));
  color: var(--ink);
}

.toc-toggle {
  appearance: none;
  border: 1px solid var(--line);
  background: var(--paper);
  color: inherit;
  border-radius: 999px;
  padding: 0.45rem 0.8rem;
  font: inherit;
  font-family: var(--font-sans);
  font-size: 0.9rem;
}

.shell {
  width: min(var(--max), calc(100% - 2.2rem));
  margin: 0 auto;
  padding-bottom: 4rem;
}

.toc {
  margin: 1rem 0 0;
  padding: 1rem 1rem 0.4rem;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 1rem;
}

.toc-kicker,
.kicker {
  margin: 0 0 0.7rem;
  font-family: var(--font-sans);
  font-size: 0.78rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
}

.toc ol {
  margin: 0;
  padding: 0 0 0.6rem 1.1rem;
}

.toc a {
  display: inline-block;
  padding: 0.28rem 0;
  color: inherit;
  text-decoration: none;
}

.toc a[aria-current="page"] {
  color: var(--accent);
}

.chapter {
  padding-top: 1.4rem;
}

.chapter h1,
.chapter h2,
.chapter h3 {
  line-height: 1.25;
  font-weight: 650;
  letter-spacing: -0.02em;
}

.chapter h1 { font-size: 2rem; margin: 0 0 1rem; }
.chapter h2 { font-size: 1.35rem; margin: 2.1rem 0 0.7rem; }
.chapter h3 { font-size: 1.15rem; margin: 1.6rem 0 0.5rem; }

.chapter p,
.chapter li {
  max-width: 40rem;
}

.chapter p { margin: 0 0 1rem; }
.chapter ul,
.chapter ol { padding-left: 1.2rem; }
.chapter li { margin: 0.35rem 0; }
.chapter a { color: var(--accent); }

.chapter pre,
.chapter table,
.mermaid {
  display: block;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.chapter pre,
.chapter code {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.88rem;
}

.chapter pre {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 0.9rem;
  padding: 0.9rem 1rem;
}

.chapter :not(pre) > code {
  background: color-mix(in srgb, var(--paper) 70%, var(--bg));
  padding: 0.08rem 0.28rem;
  border-radius: 0.3rem;
}

.chapter table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
  margin: 1rem 0 1.4rem;
}

.chapter th,
.chapter td {
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
  padding: 0.45rem 0.5rem 0.45rem 0;
}

.mermaid {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 1rem;
  padding: 0.8rem;
  margin: 1.2rem 0;
}

.pager {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.8rem;
  margin-top: 2.4rem;
  padding-top: 1.2rem;
  border-top: 1px solid var(--line);
}

.pager-link {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
  padding: 0.9rem;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 1rem;
  color: inherit;
  text-decoration: none;
  min-height: 4.5rem;
}

.pager-link.next { text-align: right; }
.pager-link span {
  font-family: var(--font-sans);
  font-size: 0.75rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
}

@media (min-width: 860px) {
  body { font-size: 1.2rem; }
  .shell { width: min(72rem, calc(100% - 4rem)); display: grid; grid-template-columns: 16rem 1fr; gap: 3rem; }
  .toc { position: sticky; top: 5rem; display: block !important; height: max-content; }
  .toc-toggle { display: none; }
  .chapter h1 { font-size: 2.5rem; }
}