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

:root {
  /* Light mode (default) */
  --bg-primary: #ffffff;
  --bg-secondary: #f8f9fa;
  --bg-card: #ffffff;
  --bg-card-hover: #f0f4ff;
  --bg-code: #f1f3f5;
  --bg-badge: #e8f4fd;
  --bg-hero: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  --bg-nav: rgba(255,255,255,0.92);
  --text-primary: #1a1a2e;
  --text-secondary: #4a5568;
  --text-muted: #718096;
  --text-on-accent: #ffffff;
  --border-color: #e2e8f0;
  --border-card: #e2e8f0;
  --accent: #667eea;
  --accent-hover: #5a6fd6;
  --accent-light: #ebf0ff;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 14px rgba(0,0,0,0.08);
  --shadow-lg: 0 10px 40px rgba(0,0,0,0.1);
  --shadow-card: 0 2px 8px rgba(0,0,0,0.06);
  --radius: 12px;
  --radius-lg: 20px;
  --song-bg: #fffbeb;
  --song-border: #f59e0b;
  --song-icon-bg: #fef3c7;
  --tag-bg: #e0e7ff;
  --tag-text: #4338ca;
  --difficulty-beginner: #10b981;
  --difficulty-intermediate: #f59e0b;
  --difficulty-advanced: #ef4444;
  --section-alt-bg: #f0f4ff;
  --toc-bg: #f8fafc;
  --toc-active: #667eea;
  --scrollbar-track: #f1f1f1;
  --scrollbar-thumb: #c1c1c1;

  /* Component variables */
  --card-bg: #ffffff;
  --accent-pale: #4338ca;
  --accent-bg: rgba(102, 126, 234, 0.08);
  --hover-bg: rgba(0, 0, 0, 0.04);
  --text-dimmed: #a0aec0;
  --bg-header: rgba(255, 255, 255, 0.92);
  --nav-link-color: #4a5568;
  --footer-color: #718096;
  --search-bg: #f8f9fa;
  --table-header-bg: #f0f4ff;
}

[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-card: #1e293b;
  --bg-card-hover: #2d3a4f;
  --bg-code: #2d3748;
  --bg-badge: #1e3a5f;
  --bg-hero: linear-gradient(135deg, #1e3a5f 0%, #2d1b4e 100%);
  --bg-nav: rgba(15,23,42,0.92);
  --text-primary: #e2e8f0;
  --text-secondary: #a0aec0;
  --text-muted: #718096;
  --text-on-accent: #ffffff;
  --border-color: #2d3748;
  --border-card: #2d3748;
  --accent: #818cf8;
  --accent-hover: #a5b4fc;
  --accent-light: #1e1b4b;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 14px rgba(0,0,0,0.3);
  --shadow-lg: 0 10px 40px rgba(0,0,0,0.4);
  --shadow-card: 0 2px 8px rgba(0,0,0,0.3);
  --song-bg: #1c1917;
  --song-border: #d97706;
  --song-icon-bg: #451a03;
  --tag-bg: #312e81;
  --tag-text: #c7d2fe;
  --difficulty-beginner: #34d399;
  --difficulty-intermediate: #fbbf24;
  --difficulty-advanced: #f87171;
  --section-alt-bg: #162032;
  --toc-bg: #1e293b;
  --toc-active: #818cf8;
  --scrollbar-track: #1e293b;
  --scrollbar-thumb: #475569;

  /* Component variables */
  --card-bg: #1e293b;
  --accent-pale: #a5b4fc;
  --accent-bg: rgba(129, 140, 248, 0.1);
  --hover-bg: rgba(255, 255, 255, 0.05);
  --text-dimmed: #4a5568;
  --bg-header: rgba(15, 23, 42, 0.92);
  --nav-link-color: #a0aec0;
  --footer-color: #4a5568;
  --search-bg: #1e293b;
  --table-header-bg: #1a2332;
}

html { scroll-behavior: smooth; scroll-padding-top: 80px; }
body {
  font-family: 'Inter', 'Noto Sans JP', system-ui, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  transition: background 0.3s, color 0.3s;
}

/* ===== Scrollbar ===== */
::-webkit-scrollbar { width: 8px; }
::-webkit-scrollbar-track { background: var(--scrollbar-track); }
::-webkit-scrollbar-thumb { background: var(--scrollbar-thumb); border-radius: 4px; }

/* ===== Navigation ===== */
.navbar {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  background: var(--bg-nav);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
  padding: 0 2rem;
  height: 64px;
  display: flex; align-items: center; justify-content: space-between;
  transition: background 0.3s, border 0.3s;
}
.navbar-brand {
  font-size: 1.25rem; font-weight: 800;
  background: linear-gradient(135deg, var(--accent), #a855f7);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text;
  display: flex; align-items: center; gap: 0.5rem;
  text-decoration: none;
}
.navbar-brand span { font-size: 1.4rem; }
.navbar-links { display: flex; align-items: center; gap: 1.5rem; list-style: none; }
.navbar-links a {
  text-decoration: none; color: var(--text-secondary);
  font-size: 0.9rem; font-weight: 500;
  transition: color 0.2s;
}
.navbar-links a:hover { color: var(--accent); }
.theme-toggle {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 50%; width: 40px; height: 40px;
  display: flex; align-items: center; justify-content: center;
  cursor: pointer; font-size: 1.2rem;
  transition: all 0.3s;
}
.theme-toggle:hover { border-color: var(--accent); transform: rotate(20deg); }

/* ===== Hero ===== */
.hero {
  margin-top: 64px;
  background: var(--bg-hero);
  padding: 5rem 2rem 4rem;
  text-align: center;
  position: relative;
  overflow: hidden;
}
.hero::before {
  content: '';
  position: absolute; inset: 0;
  background: url("data:image/svg+xml,%3Csvg width='60' height='60' viewBox='0 0 60 60' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' fill-rule='evenodd'%3E%3Cg fill='%23ffffff' fill-opacity='0.05'%3E%3Cpath d='M36 34v-4h-2v4h-4v2h4v4h2v-4h4v-2h-4zm0-30V0h-2v4h-4v2h4v4h2V6h4V4h-4zM6 34v-4H4v4H0v2h4v4h2v-4h4v-2H6zM6 4V0H4v4H0v2h4v4h2V6h4V4H6z'/%3E%3C/g%3E%3C/g%3E%3C/svg%3E");
}
.hero-content { position: relative; z-index: 1; max-width: 800px; margin: 0 auto; }
.hero h1 {
  font-size: 3.2rem; font-weight: 900; color: #fff;
  margin-bottom: 1rem; letter-spacing: -0.02em;
  line-height: 1.2;
}
.hero p { font-size: 1.2rem; color: rgba(255,255,255,0.85); max-width: 600px; margin: 0 auto 2rem; }
.hero-stats {
  display: flex; justify-content: center; gap: 3rem;
  margin-top: 2.5rem;
}
.hero-stat { text-align: center; }
.hero-stat-number { font-size: 2.2rem; font-weight: 800; color: #fff; }
.hero-stat-label { font-size: 0.85rem; color: rgba(255,255,255,0.7); margin-top: 0.25rem; }

/* ===== Table of Contents ===== */
.toc-section {
  max-width: 1100px; margin: -2rem auto 3rem; padding: 0 2rem;
  position: relative; z-index: 10;
}
.toc-card {
  background: var(--bg-card);
  border: 1px solid var(--border-card);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--shadow-lg);
}
.toc-title { font-size: 1.1rem; font-weight: 700; margin-bottom: 1.2rem; color: var(--text-primary); }
.toc-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 0.6rem;
}
.toc-item {
  display: flex; align-items: center; gap: 0.6rem;
  padding: 0.6rem 0.8rem;
  border-radius: 8px;
  text-decoration: none;
  color: var(--text-secondary);
  font-size: 0.88rem;
  font-weight: 500;
  transition: all 0.2s;
}
.toc-item:hover {
  background: var(--accent-light);
  color: var(--accent);
}
.toc-num {
  width: 26px; height: 26px;
  background: var(--accent-light);
  color: var(--accent);
  border-radius: 6px;
  display: flex; align-items: center; justify-content: center;
  font-size: 0.75rem; font-weight: 700;
  flex-shrink: 0;
}

/* ===== Main Content ===== */
.main-content { max-width: 1100px; margin: 0 auto; padding: 0 2rem 4rem; }

/* ===== Section ===== */
.theory-section {
  margin-bottom: 4rem;
  scroll-margin-top: 80px;
}
.section-header {
  display: flex; align-items: center; gap: 1rem;
  margin-bottom: 1.5rem;
  padding-bottom: 1rem;
  border-bottom: 2px solid var(--border-color);
}
.section-icon {
  width: 48px; height: 48px;
  background: var(--accent-light);
  border-radius: var(--radius);
  display: flex; align-items: center; justify-content: center;
  font-size: 1.5rem;
  flex-shrink: 0;
}
.section-title-group { flex: 1; }
.section-title {
  font-size: 1.6rem; font-weight: 800;
  color: var(--text-primary);
  line-height: 1.3;
}
.section-subtitle {
  font-size: 0.85rem; color: var(--text-muted);
  margin-top: 0.2rem;
}
.difficulty-badge {
  padding: 0.3rem 0.8rem;
  border-radius: 20px;
  font-size: 0.75rem;
  font-weight: 600;
  flex-shrink: 0;
}
.difficulty-beginner { background: #d1fae5; color: #065f46; }
.difficulty-intermediate { background: #fef3c7; color: #92400e; }
.difficulty-advanced { background: #fee2e2; color: #991b1b; }
[data-theme="dark"] .difficulty-beginner { background: #064e3b; color: #6ee7b7; }
[data-theme="dark"] .difficulty-intermediate { background: #78350f; color: #fcd34d; }
[data-theme="dark"] .difficulty-advanced { background: #7f1d1d; color: #fca5a5; }

.section-body { font-size: 0.95rem; color: var(--text-secondary); line-height: 1.8; }
.section-body p { margin-bottom: 1rem; }
.section-body h4 {
  font-size: 1.05rem; font-weight: 700;
  color: var(--text-primary);
  margin: 1.5rem 0 0.75rem;
}

/* Detail cards inside sections */
.detail-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1rem;
  margin: 1.2rem 0;
}
.detail-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-card);
  border-radius: var(--radius);
  padding: 1.2rem;
  transition: all 0.2s;
}
.detail-card:hover { transform: translateY(-2px); box-shadow: var(--shadow-md); }
.detail-card-title {
  font-size: 0.95rem; font-weight: 700;
  color: var(--accent);
  margin-bottom: 0.5rem;
  display: flex; align-items: center; gap: 0.5rem;
}
.detail-card-body { font-size: 0.88rem; color: var(--text-secondary); line-height: 1.7; }

/* Key / Scale chips */
.chip-list { display: flex; flex-wrap: wrap; gap: 0.5rem; margin: 0.8rem 0; }
.chip {
  background: var(--tag-bg);
  color: var(--tag-text);
  padding: 0.3rem 0.75rem;
  border-radius: 20px;
  font-size: 0.8rem;
  font-weight: 600;
}

/* Code-like notation */
.notation {
  display: inline-block;
  background: var(--bg-code);
  border-radius: 6px;
  padding: 0.15rem 0.5rem;
  font-family: 'Fira Code', monospace;
  font-size: 0.85rem;
  color: var(--accent);
}

/* ===== Song Examples ===== */
.song-examples {
  margin-top: 1.5rem;
  border: 1px solid var(--song-border);
  border-radius: var(--radius);
  background: var(--song-bg);
  overflow: hidden;
}
.song-examples-header {
  background: var(--song-icon-bg);
  padding: 0.8rem 1.2rem;
  font-size: 0.9rem; font-weight: 700;
  color: var(--song-border);
  display: flex; align-items: center; gap: 0.5rem;
  border-bottom: 1px solid var(--song-border);
}
.song-list { list-style: none; padding: 0; }
.song-item {
  padding: 1rem 1.2rem;
  border-bottom: 1px solid rgba(245,158,11,0.15);
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 0.5rem;
  align-items: start;
}
.song-item:last-child { border-bottom: none; }
.song-name {
  font-weight: 700; font-size: 0.92rem;
  color: var(--text-primary);
}
.song-artist {
  font-size: 0.82rem; color: var(--text-muted);
  margin-top: 0.15rem;
}
.song-desc {
  font-size: 0.82rem; color: var(--text-secondary);
  margin-top: 0.35rem;
  line-height: 1.6;
  grid-column: 1 / -1;
}
.song-genre {
  font-size: 0.72rem;
  padding: 0.2rem 0.6rem;
  border-radius: 12px;
  background: var(--tag-bg);
  color: var(--tag-text);
  font-weight: 600;
  white-space: nowrap;
  align-self: center;
}

/* ===== Tips / Callouts ===== */
.callout {
  border-left: 4px solid var(--accent);
  background: var(--accent-light);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 1rem 1.2rem;
  margin: 1.2rem 0;
  font-size: 0.9rem;
  color: var(--text-secondary);
}
.callout-title {
  font-weight: 700;
  color: var(--accent);
  margin-bottom: 0.3rem;
  display: flex; align-items: center; gap: 0.4rem;
}

/* ===== Footer ===== */
.site-footer {
  border-top: 1px solid var(--border-color);
  text-align: center;
  padding: 2rem;
  color: var(--text-muted);
  font-size: 0.85rem;
  background: var(--bg-secondary);
}

/* ===== Responsive ===== */
@media (max-width: 768px) {
  .hero h1 { font-size: 2rem; }
  .hero { padding: 3rem 1.5rem 2.5rem; }
  .hero-stats { gap: 1.5rem; }
  .hero-stat-number { font-size: 1.6rem; }
  .toc-grid { grid-template-columns: repeat(auto-fill, minmax(180px, 1fr)); }
  .navbar { padding: 0 1rem; }
  .navbar-links { display: none; }
  .main-content { padding: 0 1rem 3rem; }
  .section-header { flex-wrap: wrap; }
  .detail-grid { grid-template-columns: 1fr; }
  .song-item { grid-template-columns: 1fr; }
  .song-genre { justify-self: start; }
}