/* ===== CSS Custom Properties (Light/Dark) ===== */
:root {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f1f5f9;
  --bg-code: #1e293b;
  --text-primary: #1e293b;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --accent: #7c3aed;
  --accent-hover: #6d28d9;
  --accent-light: #ede9fe;
  --border: #e2e8f0;
  --border-strong: #cbd5e1;
  --heading-bg: linear-gradient(135deg, #7c3aed 0%, #4f46e5 100%);
  --heading-text: #ffffff;
  --link: #7c3aed;
  --link-hover: #6d28d9;
  --code-text: #a5f3fc;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.1);
  --shadow-lg: 0 8px 30px rgba(0,0,0,0.12);
  --radius: 10px;
  --radius-sm: 6px;
  --nav-bg: rgba(255,255,255,0.85);
  --nav-border: rgba(226,232,240,0.8);
  --blockquote-bg: #f1f5f9;
  --table-header-bg: #f8fafc;
  --table-stripe: #fafbfc;
  --example-bg: #eff6ff;
  --example-border: #3b82f6;
  --analogy-bg: #fffbeb;
  --analogy-border: #f59e0b;
  --activity-bg: #faf5ff;
  --activity-border: #a855f7;
}

[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #1e293b;
  --bg-code: #0f172a;
  --text-primary: #e2e8f0;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --accent: #a78bfa;
  --accent-hover: #c4b5fd;
  --accent-light: rgba(167,139,250,0.15);
  --border: #334155;
  --border-strong: #475569;
  --heading-bg: linear-gradient(135deg, #7c3aed 0%, #4f46e5 100%);
  --heading-text: #ffffff;
  --link: #a78bfa;
  --link-hover: #c4b5fd;
  --code-text: #67e8f9;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.4);
  --shadow-lg: 0 8px 30px rgba(0,0,0,0.5);
  --nav-bg: rgba(15,23,42,0.9);
  --nav-border: rgba(51,65,85,0.8);
  --blockquote-bg: #1e293b;
  --table-header-bg: #1e293b;
  --table-stripe: #162032;
  --example-bg: rgba(59,130,246,0.1);
  --example-border: #3b82f6;
  --analogy-bg: rgba(245,158,11,0.1);
  --analogy-border: #f59e0b;
  --activity-bg: rgba(168,85,247,0.1);
  --activity-border: #a855f7;
}

/* ===== Reset ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

/* ===== Base ===== */
html { scroll-behavior: smooth; }

body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  font-size: 1rem;
  line-height: 1.7;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  transition: background-color 0.3s, color 0.3s;
  min-height: 100vh;
}

/* ===== Site Navigation ===== */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: var(--nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--nav-border);
  padding: 0 1.5rem;
}

.site-nav-inner {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 56px;
  gap: 1rem;
}

.site-nav-brand {
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--accent);
  text-decoration: none;
  white-space: nowrap;
}
.site-nav-brand:hover { color: var(--accent-hover); }

.site-nav-links {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  flex-wrap: wrap;
}
.site-nav-links a {
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 0.85rem;
  padding: 0.35rem 0.65rem;
  border-radius: var(--radius-sm);
  transition: background 0.2s, color 0.2s;
  white-space: nowrap;
}
.site-nav-links a:hover {
  background: var(--accent-light);
  color: var(--accent);
}

/* Hamburger */
.nav-toggle { display: none; background: none; border: none; cursor: pointer; padding: 0.5rem; color: var(--text-primary); }
.nav-toggle svg { display: block; }

/* Dark Mode Toggle */
.theme-toggle {
  background: none;
  border: 2px solid var(--border);
  border-radius: 50%;
  width: 38px;
  height: 38px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.15rem;
  transition: border-color 0.2s, background 0.2s;
  color: var(--text-primary);
  flex-shrink: 0;
}
.theme-toggle:hover {
  border-color: var(--accent);
  background: var(--accent-light);
}

/* ===== Main Content ===== */
main {
  max-width: 900px;
  margin: 0 auto;
  padding: 2rem 1.5rem 3rem;
}

/* ===== Typography ===== */
h1, h2, h3, h4 {
  font-weight: 700;
  line-height: 1.3;
  color: var(--heading-text);
  background: var(--heading-bg);
  padding: 0.75rem 1.25rem;
  border-radius: var(--radius);
  margin: 2rem 0 1rem;
}

h1 {
  font-size: clamp(1.6rem, 4vw, 2.25rem);
  text-align: center;
  margin-top: 1rem;
}
h2 { font-size: clamp(1.25rem, 3vw, 1.6rem); }
h3 { font-size: clamp(1.05rem, 2.5vw, 1.3rem); }
h4 { font-size: 1.1rem; }

p {
  margin: 0.75rem 0;
  color: var(--text-primary);
}

strong { font-weight: 700; color: var(--text-primary); }
em { font-style: italic; }

a { color: var(--link); transition: color 0.2s; }
a:hover { color: var(--link-hover); }

/* ===== Lists ===== */
ul, ol { margin: 0.5rem 0 0.5rem 1.5rem; }
ul { list-style-type: disc; }
ol { list-style-type: decimal; }
li { padding: 0.3rem 0; color: var(--text-primary); }
li ul, li ol { margin-top: 0.25rem; }
dl { margin: 0.5rem 0 0.5rem 1rem; }
dd { margin-left: 1.25rem; padding-bottom: 0.5rem; color: var(--text-secondary); }

/* ===== Code ===== */
code {
  font-family: 'Cascadia Code', 'Fira Code', 'JetBrains Mono', monospace;
  font-size: 0.9em;
  background: var(--bg-code);
  color: var(--code-text);
  padding: 0.15em 0.4em;
  border-radius: 4px;
}

pre {
  background: var(--bg-code);
  color: var(--code-text);
  padding: 1.25rem;
  border-radius: var(--radius);
  overflow-x: auto;
  margin: 1rem 0;
  line-height: 1.6;
  font-size: 0.9rem;
}
pre code {
  background: none;
  padding: 0;
  font-size: inherit;
}

.code-comment { color: #67e8f9; font-style: italic; }

/* ===== Tables ===== */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0;
  font-size: 0.95rem;
  border-radius: var(--radius);
  overflow: hidden;
  border: 1px solid var(--border);
}
th, td {
  padding: 0.75rem 1rem;
  text-align: left;
  border: 1px solid var(--border);
  color: var(--text-primary);
}
th {
  background: var(--table-header-bg);
  font-weight: 600;
}
tr:nth-child(even) { background: var(--table-stripe); }

.comparison-table { width: 100%; margin: 1rem 0; }
.comparison-table th, .comparison-table td { padding: 0.75rem 1rem; text-align: left; border: 1px solid var(--border); }
.comparison-table th { background: var(--table-header-bg); font-weight: 600; }

/* ===== Blockquotes ===== */
blockquote {
  background: var(--blockquote-bg);
  border-left: 4px solid var(--accent);
  padding: 1rem 1.5rem;
  margin: 1rem 0;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  color: var(--text-secondary);
}

/* ===== Callout Boxes ===== */
.example-box {
  background: var(--example-bg);
  border-left: 4px solid var(--example-border);
  padding: 1rem 1.25rem;
  margin: 1rem 0;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}
.analogy-box {
  background: var(--analogy-bg);
  border-left: 4px solid var(--analogy-border);
  padding: 1rem 1.25rem;
  margin: 1rem 0;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}
.activity-box {
  background: var(--activity-bg);
  border-left: 4px solid var(--activity-border);
  padding: 1rem 1.25rem;
  margin: 1rem 0;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}
.comment-block {
  border-left: 4px solid var(--accent);
  padding: 0.75rem 1rem;
  margin: 1rem 0;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  background: var(--bg-tertiary);
}
.dice-visual {
  background: var(--bg-tertiary);
  padding: 1.25rem;
  border-radius: var(--radius);
  margin: 1rem 0;
}

/* ===== Images / SVGs ===== */
img { max-width: 100%; height: auto; border-radius: var(--radius-sm); }
div img { max-width: 45%; }
svg { display: block; margin: 0 auto; max-width: 100%; }
.center { text-align: center; }

/* ===== Mermaid ===== */
.mermaid_container, .mermaid-diagram, .mermaid {
  margin: 1.5rem auto;
  padding: 1.25rem;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  max-width: 100%;
  text-align: center;
  overflow-x: auto;
}
.mermaid svg { margin: 0 auto; display: block; }

/* ===== Footer ===== */
footer {
  max-width: 900px;
  margin: 0 auto;
  padding: 1.5rem;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.9rem;
}

/* ===== Prev / Next Navigation ===== */
.page-nav {
  display: flex;
  justify-content: space-between;
  align-items: stretch;
  gap: 1rem;
  margin: 3rem 0 1rem;
  max-width: 900px;
  margin-left: auto;
  margin-right: auto;
  padding: 0 1.5rem;
}
.page-nav a {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
  text-decoration: none;
  padding: 1rem 1.25rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-secondary);
  transition: border-color 0.2s, box-shadow 0.2s;
  min-width: 0;
  flex: 1;
  max-width: 48%;
}
.page-nav a:hover {
  border-color: var(--accent);
  box-shadow: var(--shadow-sm);
}
.page-nav a.next { text-align: right; margin-left: auto; }
.page-nav-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
}
.page-nav-title {
  font-weight: 600;
  color: var(--accent);
  font-size: 0.95rem;
}

/* ===== Sup / Sub ===== */
sup { font-size: 0.7em; vertical-align: super; }
sub { font-size: 0.7em; vertical-align: sub; }

/* ===== Mobile ===== */
@media (max-width: 768px) {
  main { padding: 1.25rem 1rem 2rem; }

  .site-nav-links {
    display: none;
    position: absolute;
    top: 56px;
    left: 0;
    right: 0;
    background: var(--nav-bg);
    backdrop-filter: blur(12px);
    flex-direction: column;
    padding: 0.5rem;
    border-bottom: 1px solid var(--nav-border);
    gap: 0;
  }
  .site-nav-links.open { display: flex; }
  .site-nav-links a { padding: 0.65rem 1rem; width: 100%; }
  .nav-toggle { display: block; }

  h1, h2, h3, h4 { padding: 0.6rem 1rem; }

  .page-nav { flex-direction: column; padding: 0 1rem; }
  .page-nav a { max-width: 100%; }
  .page-nav a.next { text-align: left; }

  table { font-size: 0.85rem; display: block; overflow-x: auto; }

  div img { max-width: 100%; }
}

@media (max-width: 480px) {
  .site-nav-inner { padding: 0; }
  main { padding: 1rem 0.75rem 2rem; }
}