/* ===== Theme Variables ===== */
:root, [data-theme="dark"] {
  --bg-body: #0d1117; --bg-header: #161b22; --bg-surface: #161b22; --bg-hover: #21262d;
  --border: #30363d; --border-light: #21262d;
  --text-primary: #e6edf3; --text-secondary: #c9d1d9; --text-muted: #8b949e;
  --accent: #1f6feb; --accent-text: #58a6ff; --accent-bg: #0d2137;
  --code-bg: #161b22; --code-text: #79c0ff;
  --label-color: #6e40c9;
  --tag-bg: #1f6feb22; --tag-border: #1f6feb44;
  --notes-bg: #1c1a10; --notes-border: #d29922; --notes-text: #8b8070;
  --dot-bg: #30363d; --prog-bg: #1f6feb;
  --callout-bg: #1c2128; --quote-bg: #0d2137;
  --lesson-hover: #1c2128; --num-color: #565f89;
  --slides-border: #8957e544; --slides-text: #d2a8ff;
  --slides-hover-bg: #8957e522; --slides-hover-border: #8957e5;
}
[data-theme="light"] {
  --bg-body: #ffffff; --bg-header: #f6f8fa; --bg-surface: #f6f8fa; --bg-hover: #eaeef2;
  --border: #d0d7de; --border-light: #d8dee4;
  --text-primary: #1f2328; --text-secondary: #32383f; --text-muted: #656d76;
  --accent: #0969da; --accent-text: #0969da; --accent-bg: #ddf4ff;
  --code-bg: #f6f8fa; --code-text: #0550ae;
  --label-color: #8250df;
  --tag-bg: #ddf4ff; --tag-border: #54aeff66;
  --notes-bg: #fff8c5; --notes-border: #d4a72c; --notes-text: #6d5c00;
  --dot-bg: #d0d7de; --prog-bg: #0969da;
  --callout-bg: #f6f8fa; --quote-bg: #ddf4ff;
  --lesson-hover: #f0f2f5; --num-color: #8b949e;
  --slides-border: #8250df44; --slides-text: #8250df;
  --slides-hover-bg: #8250df22; --slides-hover-border: #8250df;
}
[data-theme="grey"] {
  --bg-body: #2b2b2b; --bg-header: #353535; --bg-surface: #353535; --bg-hover: #404040;
  --border: #505050; --border-light: #454545;
  --text-primary: #e0e0e0; --text-secondary: #c0c0c0; --text-muted: #999999;
  --accent: #6a9fd8; --accent-text: #7cb3e8; --accent-bg: #2a3a4a;
  --code-bg: #353535; --code-text: #7cb3e8;
  --label-color: #b388d9;
  --tag-bg: #6a9fd822; --tag-border: #6a9fd844;
  --notes-bg: #3a3520; --notes-border: #c9a227; --notes-text: #a09070;
  --dot-bg: #505050; --prog-bg: #6a9fd8;
  --callout-bg: #353535; --quote-bg: #2a3a4a;
  --lesson-hover: #3a3a3a; --num-color: #777;
  --slides-border: #b388d944; --slides-text: #b388d9;
  --slides-hover-bg: #b388d922; --slides-hover-border: #b388d9;
}
[data-theme="pink"] {
  --bg-body: #1a1020; --bg-header: #231530; --bg-surface: #231530; --bg-hover: #2e1d3d;
  --border: #3d2a50; --border-light: #342345;
  --text-primary: #f0e0f5; --text-secondary: #d4bfdd; --text-muted: #a088b0;
  --accent: #d946ef; --accent-text: #e879f9; --accent-bg: #2a1035;
  --code-bg: #231530; --code-text: #e879f9;
  --label-color: #c084fc;
  --tag-bg: #d946ef22; --tag-border: #d946ef44;
  --notes-bg: #2a1a20; --notes-border: #f472b6; --notes-text: #b08090;
  --dot-bg: #3d2a50; --prog-bg: #d946ef;
  --callout-bg: #231530; --quote-bg: #2a1035;
  --lesson-hover: #2a1535; --num-color: #8060a0;
  --slides-border: #c084fc44; --slides-text: #c084fc;
  --slides-hover-bg: #c084fc22; --slides-hover-border: #c084fc;
}
[data-theme="green"] {
  --bg-body: #0a0f0a; --bg-header: #0f170f; --bg-surface: #0f170f; --bg-hover: #162016;
  --border: #1e3a1e; --border-light: #162c16;
  --text-primary: #33ff33; --text-secondary: #20cc20; --text-muted: #1a9a1a;
  --accent: #00cc00; --accent-text: #33ff33; --accent-bg: #0a1f0a;
  --code-bg: #0f170f; --code-text: #33ff33;
  --label-color: #00cc00;
  --tag-bg: #00cc0022; --tag-border: #00cc0044;
  --notes-bg: #1a1a0a; --notes-border: #99cc00; --notes-text: #708040;
  --dot-bg: #1e3a1e; --prog-bg: #00cc00;
  --callout-bg: #0f170f; --quote-bg: #0a1f0a;
  --lesson-hover: #142014; --num-color: #1a6a1a;
  --slides-border: #00cc0044; --slides-text: #33ff33;
  --slides-hover-bg: #00cc0022; --slides-hover-border: #00cc00;
}

/* ===== Shared Base ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; background: var(--bg-body); color: var(--text-primary); transition: background 0.3s, color 0.3s; }

/* ===== Theme Picker ===== */
.theme-picker { display: flex; align-items: center; gap: 6px; flex-shrink: 0; margin: 0 auto; }
.theme-picker .theme-label { color: var(--text-muted); font-size: 0.72rem; margin-right: 4px; white-space: nowrap; }
.theme-picker button { width: 18px; height: 18px; border-radius: 50%; border: 2px solid var(--border); cursor: pointer; transition: all 0.15s; padding: 0; }
.theme-picker button:hover { transform: scale(1.2); }
.theme-picker button.active { border-color: var(--accent-text); box-shadow: 0 0 0 2px var(--accent-text); }
.theme-picker .t-dark { background: #0d1117; }
.theme-picker .t-light { background: #ffffff; }
.theme-picker .t-grey { background: #2b2b2b; }
.theme-picker .t-pink { background: #1a1020; }
.theme-picker .t-green { background: #0a0f0a; }

/* ===== Shared Header ===== */
.top-header, header.top-header {
  background: var(--bg-header); border-bottom: 1px solid var(--border);
  padding: 10px 24px; display: flex; align-items: center; gap: 20px; flex-wrap: wrap; flex-shrink: 0;
  position: relative;
}

/* ===== Language Picker (top-center) ===== */
.lang-picker {
  position: absolute; left: 50%; top: 50%; transform: translate(-50%, -50%);
  display: flex; gap: 0;
  background: var(--bg-surface); border: 1px solid var(--border);
  border-radius: 20px; padding: 2px; z-index: 5;
}
.lang-picker a {
  color: var(--text-muted); text-decoration: none;
  font-size: 0.72rem; font-weight: 700; letter-spacing: 0.04em;
  padding: 4px 14px; border-radius: 18px; transition: all 0.15s;
}
.lang-picker a:hover { color: var(--text-primary); background: var(--bg-hover); text-decoration: none; }
.lang-picker a.active { color: #fff; background: var(--accent); }
.lang-picker-fixed {
  position: fixed; top: 16px; left: 50%; transform: translateX(-50%);
  display: flex; gap: 0;
  background: var(--bg-surface); border: 1px solid var(--border);
  border-radius: 20px; padding: 2px; z-index: 100;
}
.lang-picker-fixed a {
  color: var(--text-muted); text-decoration: none;
  font-size: 0.72rem; font-weight: 700; letter-spacing: 0.04em;
  padding: 4px 14px; border-radius: 18px; transition: all 0.15s;
}
.lang-picker-fixed a:hover { color: var(--text-primary); background: var(--bg-hover); text-decoration: none; }
.lang-picker-fixed a.active { color: #fff; background: var(--accent); }
@media (max-width: 960px) {
  .lang-picker { position: static; transform: none; margin: 0 auto; }
}
.lesson-badge { background: var(--accent); color: #fff; font-size: 0.72rem; font-weight: 700; padding: 3px 10px; border-radius: 20px; text-transform: uppercase; letter-spacing: 0.05em; white-space: nowrap; }
.top-header .lesson-title, header .lesson-title { font-size: 0.95rem; font-weight: 600; color: var(--text-secondary); flex: 1; }
.top-header nav { display: flex; gap: 4px; flex-wrap: wrap; }
.top-header nav a { color: var(--text-muted); text-decoration: none; font-size: 0.82rem; padding: 4px 12px; border-radius: 6px; border: 1px solid transparent; transition: all 0.15s; }
.top-header nav a:hover { color: var(--text-primary); background: var(--bg-hover); }
.top-header nav a.active { color: var(--accent-text); border-color: var(--accent); background: var(--accent-bg); }

/* ===== Code Blocks ===== */
.code-wrap { position: relative; }
.code-wrap .copy-btn { position: absolute; top: 8px; right: 8px; background: var(--bg-hover); border: 1px solid var(--border); color: var(--text-muted); font-size: 0.7rem; padding: 3px 10px; border-radius: 5px; cursor: pointer; opacity: 0; transition: opacity 0.15s; z-index: 2; }
.code-wrap:hover .copy-btn { opacity: 1; }
.code-wrap .copy-btn:hover { background: var(--border); color: var(--text-primary); }
.code-wrap .copy-btn.copied { color: #2ea043; border-color: #2ea043; }
code:not(pre code) { font-family: 'SF Mono','Fira Code',monospace; font-size: 0.83em; background: var(--code-bg); border: 1px solid var(--border); padding: 2px 6px; border-radius: 4px; color: var(--code-text); }

/* ===== Tables ===== */
table { border-collapse: collapse; width: 100%; }
th { background: var(--bg-surface); color: var(--text-primary); padding: 10px 14px; text-align: left; border-bottom: 2px solid var(--border); }
td { padding: 10px 14px; border-bottom: 1px solid var(--border-light); color: var(--text-muted); }
tr:last-child td { border-bottom: none; }

/* ===== Links ===== */
a { color: var(--accent-text); }
a:hover { text-decoration: underline; }

/* ===== Print / PDF ===== */
@media print {
  :root, [data-theme] {
    --bg-body: #fff; --bg-header: #f6f8fa; --bg-surface: #f6f8fa; --bg-hover: #eaeef2;
    --border: #d0d7de; --border-light: #d8dee4;
    --text-primary: #1f2328; --text-secondary: #32383f; --text-muted: #656d76;
    --accent: #0969da; --accent-text: #0969da; --accent-bg: #ddf4ff;
    --code-bg: #f6f8fa; --code-text: #0550ae;
    --label-color: #8250df;
    --tag-bg: #ddf4ff; --tag-border: #54aeff66;
    --notes-bg: #fff8c5; --notes-border: #d4a72c; --notes-text: #6d5c00;
    --callout-bg: #f6f8fa; --quote-bg: #ddf4ff;
  }
  .top-header, #slide-nav, .theme-picker, .lang-picker, .lang-picker-fixed,
  .copy-btn, .pdf-download, .lesson-links .pdf-link { display: none !important; }
  body { background: #fff !important; }
}