:root {
  --bg: #ffffff;
  --bg-card: #f8f9fa;
  --text: #1a1a2e;
  --text-secondary: #555;
  --accent: #0a0a23;
  --accent-light: #3b3b4f;
  --border: #e0e0e0;
  --nav-bg: #0a0a23;
  --nav-text: #ffffff;
  --link: #0056b3;
  --code-bg: #e8e8e8;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #1a1a2e;
    --bg-card: #16213e;
    --text: #e0e0e0;
    --text-secondary: #aaa;
    --accent: #ffc107;
    --accent-light: #ffda57;
    --border: #333;
    --nav-bg: #0f0f1a;
    --nav-text: #ffc107;
    --link: #7cb8ff;
    --code-bg: #2a2a3e;
  }
}

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

html { scroll-behavior: smooth; }

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Noto Sans', 'Noto Sans JP', 'Noto Sans KR', 'Noto Sans SC', 'Noto Sans TC', sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
}

/* Nav */
nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--nav-bg);
  color: var(--nav-text);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.6rem 1.5rem;
  box-shadow: 0 2px 8px rgba(0,0,0,0.15);
}

nav .logo {
  font-size: 1.2rem;
  font-weight: 700;
  letter-spacing: 0.5px;
}

nav .nav-links {
  display: flex;
  gap: 1rem;
  align-items: center;
  flex-wrap: wrap;
}

nav .nav-links a {
  color: var(--nav-text);
  text-decoration: none;
  font-size: 0.85rem;
  opacity: 0.85;
  transition: opacity 0.2s;
}

nav .nav-links a:hover { opacity: 1; }

#lang-select {
  padding: 0.3rem 0.5rem;
  border-radius: 4px;
  border: 1px solid rgba(255,255,255,0.3);
  background: rgba(255,255,255,0.1);
  color: var(--nav-text);
  font-size: 0.85rem;
  cursor: pointer;
}

#lang-select option { color: #000; background: #fff; }

/* Main */
main {
  max-width: 860px;
  margin: 0 auto;
  padding: 2rem 1.5rem 4rem;
}

section {
  margin-bottom: 2.5rem;
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 2rem;
  margin-bottom: 1.5rem;
}

h1 {
  font-size: 2rem;
  color: var(--accent);
  margin-bottom: 0.5rem;
}

h2 {
  font-size: 1.4rem;
  color: var(--accent);
  margin-bottom: 1rem;
  padding-bottom: 0.4rem;
  border-bottom: 2px solid var(--accent);
}

h3 {
  font-size: 1.1rem;
  margin: 1.2rem 0 0.5rem;
  color: var(--text);
}

p { margin-bottom: 0.8rem; }

ul, ol {
  margin: 0.5rem 0 1rem 1.5rem;
}

li { margin-bottom: 0.3rem; }

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

code {
  background: var(--code-bg);
  padding: 0.15rem 0.4rem;
  border-radius: 3px;
  font-size: 0.9em;
}

pre {
  background: var(--code-bg);
  padding: 1rem;
  border-radius: 6px;
  overflow-x: auto;
  font-size: 0.85rem;
  margin: 1rem 0;
  white-space: pre-wrap;
}

.subtitle {
  color: var(--text-secondary);
  font-size: 1.05rem;
  margin-bottom: 1.5rem;
}

.bgm-list {
  columns: 2;
  column-gap: 2rem;
  font-size: 0.9rem;
}

.bgm-list li { break-inside: avoid; }

footer {
  text-align: center;
  padding: 2rem;
  color: var(--text-secondary);
  font-size: 0.85rem;
  border-top: 1px solid var(--border);
}

/* Responsive */
@media (max-width: 600px) {
  nav { flex-direction: column; gap: 0.5rem; }
  nav .nav-links { justify-content: center; }
  .bgm-list { columns: 1; }
  .card { padding: 1.2rem; }
  h1 { font-size: 1.6rem; }
}