:root {
  --bg: #fafafa;
  --fg: #1a1a1a;
  --muted: #666;
  --border: #e0e0e0;
  --accent: #2563eb;
  --accent-light: #eff6ff;
  --code-bg: #f3f4f6;
  --max-w: 720px;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  color: var(--fg);
  background: var(--bg);
  line-height: 1.7;
  font-size: 16px;
}

.container {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 3rem 1.5rem;
}

/* Navigation */
nav {
  border-bottom: 1px solid var(--border);
  padding: 0.75rem 0;
  margin-bottom: 2.5rem;
  display: flex;
  gap: 1.5rem;
  flex-wrap: wrap;
  align-items: center;
}

nav a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.875rem;
}

nav a:hover, nav a.active {
  color: var(--accent);
}

nav .brand {
  font-weight: 600;
  color: var(--fg);
  margin-right: auto;
}

/* Typography */
h1 { font-size: 2rem; margin-bottom: 0.5rem; letter-spacing: -0.02em; }
h2 { font-size: 1.35rem; margin: 2rem 0 0.75rem; letter-spacing: -0.01em; }
h3 { font-size: 1.1rem; margin: 1.5rem 0 0.5rem; }

p { margin-bottom: 1rem; color: var(--fg); }
.subtitle { color: var(--muted); font-size: 1.1rem; margin-bottom: 2rem; }

/* Links */
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* Code */
code {
  background: var(--code-bg);
  padding: 0.15em 0.4em;
  border-radius: 4px;
  font-size: 0.9em;
  font-family: "SF Mono", "Fira Code", monospace;
}

pre {
  background: var(--code-bg);
  padding: 1rem 1.25rem;
  border-radius: 8px;
  overflow-x: auto;
  margin-bottom: 1.5rem;
  line-height: 1.5;
}

pre code {
  background: none;
  padding: 0;
  font-size: 0.85em;
}

/* Tables */
table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: 1.5rem;
  font-size: 0.9rem;
}

th, td {
  text-align: left;
  padding: 0.5rem 0.75rem;
  border-bottom: 1px solid var(--border);
}

th { font-weight: 600; color: var(--muted); font-size: 0.8rem; text-transform: uppercase; letter-spacing: 0.05em; }

/* Cards */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 1rem;
  margin-bottom: 2rem;
}

.card {
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.25rem;
  transition: border-color 0.2s;
}

.card:hover { border-color: var(--accent); }
.card h3 { margin: 0 0 0.4rem; font-size: 1rem; }
.card p { font-size: 0.875rem; color: var(--muted); margin: 0; }
.card a { text-decoration: none; color: inherit; display: block; }

/* Diagram box */
.diagram {
  background: var(--code-bg);
  border-radius: 8px;
  padding: 1.5rem;
  margin-bottom: 1.5rem;
  font-family: "SF Mono", "Fira Code", monospace;
  font-size: 0.85rem;
  line-height: 1.6;
  white-space: pre;
  overflow-x: auto;
}

/* Stats */
.stats {
  display: flex;
  gap: 2rem;
  margin-bottom: 2rem;
  flex-wrap: wrap;
}

.stat { text-align: center; }
.stat .num { font-size: 1.75rem; font-weight: 700; color: var(--accent); display: block; }
.stat .label { font-size: 0.8rem; color: var(--muted); text-transform: uppercase; letter-spacing: 0.05em; }

/* Footer */
footer {
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.8rem;
}

/* Responsive */
@media (max-width: 600px) {
  .container { padding: 2rem 1rem; }
  h1 { font-size: 1.5rem; }
  .stats { gap: 1rem; }
  .card-grid { grid-template-columns: 1fr; }
}