:root {
  --max-width: 760px;
  --bg: #ffffff;
  --fg: #1a1a1a;
  --muted: #666;
  --accent: #1a5fb4;
  --border: #ddd;
  color-scheme: light;
}

:root[data-theme="dark"] {
  --bg: #0d1117;
  --fg: #f0f6fc;
  --muted: #9198a1;
  --accent: #58a6ff;
  --border: #30363d;
  color-scheme: dark;
}

:root[data-font-size="sm"] { font-size: 93.75%; }
:root[data-font-size="lg"] { font-size: 112.5%; }
:root[data-font-size="xl"] { font-size: 125%; }

* { box-sizing: border-box; }

body {
  font-family: -apple-system, "Segoe UI", Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--fg);
  line-height: 1.6;
  margin: 0;
}

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.25rem;
}

a { color: var(--accent); }

.site-header {
  border-bottom: 1px solid var(--border);
  padding: 1rem 0;
}
.site-header .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.site-title {
  font-weight: 700;
  text-decoration: none;
  color: var(--fg);
}
.site-header nav a {
  margin-left: 1rem;
  text-decoration: none;
}

main.container {
  padding-top: 2rem;
  padding-bottom: 3rem;
  min-height: 60vh;
}

.hero {
  text-align: center;
  padding: 4rem 0;
}
.hero-actions {
  display: flex;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
}
.hero .button {
  display: inline-block;
  margin-top: 1rem;
  padding: 0.6rem 1.2rem;
  border: 1px solid var(--accent);
  border-radius: 6px;
  text-decoration: none;
}

.breadcrumb { margin-bottom: 0.5rem; }
.breadcrumb a { text-decoration: none; color: var(--muted); }

.textbook-ref {
  color: var(--muted);
  font-style: italic;
  font-size: 0.9rem;
}

article.note img {
  max-width: 100%;
  height: auto;
  display: block;
  margin: 1rem auto;
}

article.note table {
  border-collapse: collapse;
  width: 100%;
  margin: 1rem 0;
}
article.note th, article.note td {
  border: 1px solid var(--border);
  padding: 0.4rem 0.6rem;
  text-align: left;
}

.page-nav {
  display: flex;
  justify-content: space-between;
  border-top: 1px solid var(--border);
  padding-top: 1rem;
  margin-top: 2rem;
}
.page-nav a { text-decoration: none; }

section.week { margin-bottom: 2rem; }
section.week h2 { margin-bottom: 0.5rem; }
section.week ol { padding-left: 1.25rem; }

.site-footer {
  border-top: 1px solid var(--border);
  padding: 1.5rem 0;
  color: var(--muted);
  font-size: 0.9rem;
}