:root {
  --bg: #fafaf9;
  --fg: #1c1917;
  --muted: #78716c;
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --border: #e7e5e4;
  --code-bg: #f5f5f4;
  --block-bg: #fef9c3;
  --card-bg: #ffffff;
  --shadow: 0 1px 3px rgba(0,0,0,0.06);
}
html.dark {
  --bg: #1a1a1a;
  --fg: #e7e5e4;
  --muted: #a8a29e;
  --accent: #60a5fa;
  --accent-hover: #93c5fd;
  --border: #333;
  --code-bg: #262626;
  --block-bg: #2a2517;
  --card-bg: #222;
  --shadow: 0 1px 3px rgba(0,0,0,0.3);
}
* { margin: 0; padding: 0; box-sizing: border-box; }
html { font-size: 17px; scroll-behavior: smooth; }
body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto,
    'Helvetica Neue', Arial, sans-serif;
  background: var(--bg);
  color: var(--fg);
  line-height: 1.7;
  padding: 0;
  -webkit-text-size-adjust: 100%;
}
.wrapper {
  max-width: 720px;
  margin: 0 auto;
  padding: 2rem 1.25rem 4rem;
}
.site-header {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.5rem 0.75rem;
  padding: 1.5rem 1rem 1rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 2rem;
}
.site-header-brand {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
}
.home-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  color: var(--fg);
  text-decoration: none;
  border-radius: 8px;
  padding: 0.2rem;
  line-height: 0;
  border: 1px solid transparent;
}
.home-link:hover {
  color: var(--accent);
  border-color: var(--border);
  background: var(--code-bg);
  text-decoration: none;
}
.home-link svg {
  width: 1.35rem;
  height: 1.35rem;
}
.site-title {
  color: var(--fg);
  text-decoration: none;
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
}
.site-title:hover {
  color: var(--accent);
  text-decoration: none;
}

h1 { font-size: 1.85rem; line-height: 1.25; margin: 0 0 0.5rem; font-weight: 800; letter-spacing: -0.02em; }
h2 { font-size: 1.35rem; margin: 2.5rem 0 0.75rem; font-weight: 700; letter-spacing: -0.01em; border-bottom: 1px solid var(--border); padding-bottom: 0.35rem; }
h3 { font-size: 1.1rem; margin: 2rem 0 0.5rem; font-weight: 600; }
h4 { font-size: 1rem; margin: 1.5rem 0 0.4rem; font-weight: 600; }

p { margin: 0.8rem 0; }
a { color: var(--accent); text-decoration: none; }
a:hover { color: var(--accent-hover); text-decoration: underline; }

blockquote {
  border-left: 4px solid var(--accent);
  background: var(--code-bg);
  padding: 0.75rem 1rem;
  margin: 1.25rem 0;
  border-radius: 0 6px 6px 0;
  font-style: italic;
}
blockquote p { margin: 0.3rem 0; }

ul, ol { margin: 0.8rem 0; padding-left: 1.5rem; }
li { margin: 0.3rem 0; }
li > ul, li > ol { margin: 0.2rem 0; }

code {
  font-family: 'SF Mono', 'Fira Code', 'Cascadia Code', Menlo, monospace;
  font-size: 0.88em;
  background: var(--code-bg);
  padding: 0.15em 0.35em;
  border-radius: 4px;
}
pre {
  background: var(--code-bg);
  padding: 1rem 1.15rem;
  border-radius: 8px;
  overflow-x: auto;
  margin: 1rem 0;
  border: 1px solid var(--border);
  font-size: 0.85rem;
  line-height: 1.55;
  -webkit-overflow-scrolling: touch;
}
pre code { background: none; padding: 0; font-size: inherit; }

pre.mermaid {
  background: var(--card-bg);
  text-align: center;
  border: 1px solid var(--border);
  padding: 1rem 0.5rem;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}
pre.mermaid svg {
  display: block;
  margin: 0 auto;
  max-width: 100%;
  height: auto;
  vertical-align: top;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0;
  font-size: 0.92rem;
  display: block;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}
thead { background: var(--code-bg); }
th, td {
  text-align: left;
  padding: 0.55rem 0.75rem;
  border: 1px solid var(--border);
  white-space: nowrap;
}
td { white-space: normal; }
th { font-weight: 600; white-space: nowrap; }
tr:nth-child(even) { background: var(--code-bg); }

hr { border: none; border-top: 1px solid var(--border); margin: 2rem 0; }

.subtitle {
  color: var(--muted);
  font-style: italic;
  margin-bottom: 1.5rem;
  font-size: 1.05rem;
}

.diagram-caption {
  color: var(--muted);
  font-size: 0.95rem;
  margin: 0.35rem 0 0.5rem;
}

.chapter-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.25rem 0;
  margin-top: 2.5rem;
  border-top: 1px solid var(--border);
  flex-wrap: wrap;
}
.chapter-nav a {
  display: inline-block;
  padding: 0.5rem 1rem;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 0.88rem;
  font-weight: 500;
  box-shadow: var(--shadow);
  transition: border-color 0.15s;
  max-width: 48%;
}
.chapter-nav a:hover {
  border-color: var(--accent);
  text-decoration: none;
}
.nav-prev { text-align: left; }
.nav-next { text-align: right; margin-left: auto; }

.toc-link {
  display: inline-block;
  margin-top: 1rem;
  font-size: 0.88rem;
  font-weight: 500;
}

/* ── Theme toggle ── */
.theme-toggle {
  background: none;
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
  padding: 0.3rem 0.45rem;
  line-height: 1;
  font-size: 1.1rem;
  color: var(--fg);
  transition: border-color 0.15s, background 0.15s;
  vertical-align: middle;
}
.theme-toggle:hover {
  border-color: var(--accent);
  background: var(--code-bg);
}

@media (max-width: 480px) {
  html { font-size: 16px; }
  .wrapper { padding: 1.25rem 1rem 3rem; }
  h1 { font-size: 1.55rem; }
  h2 { font-size: 1.2rem; }
  pre { font-size: 0.8rem; padding: 0.75rem; }
  .chapter-nav a { max-width: 100%; }
  th, td { padding: 0.4rem 0.5rem; font-size: 0.85rem; }
}

@media print {
  .chapter-nav, .site-header { display: none; }
  body { font-size: 11pt; }
}