:root {
  --bg: #0f1419;
  --bg-panel: #161b22;
  --bg-elev: #1c232c;
  --fg: #e6edf3;
  --fg-mute: #8b98a5;
  --accent: #6cb6ff;
  --accent-2: #f0883e;
  --ok: #4ade80;
  --warn: #fbbf24;
  --err: #f87171;
  --border: #2d333b;
  --code-bg: #0d1117;
  --shadow: 0 4px 20px rgba(0,0,0,0.4);
}
[data-theme="light"] {
  --bg: #fafbfc;
  --bg-panel: #ffffff;
  --bg-elev: #f6f8fa;
  --fg: #1f2328;
  --fg-mute: #656d76;
  --accent: #0969da;
  --accent-2: #bc4c00;
  --ok: #1a7f37;
  --warn: #9a6700;
  --err: #cf222e;
  --border: #d0d7de;
  --code-bg: #f6f8fa;
  --shadow: 0 4px 20px rgba(0,0,0,0.08);
}

* { box-sizing: border-box; }
html, body { height: 100%; margin: 0; }
body {
  font-family: -apple-system, "Segoe UI", system-ui, "Helvetica Neue", sans-serif;
  background: var(--bg);
  color: var(--fg);
  font-size: 16px;
  line-height: 1.6;
}

#app {
  display: grid;
  grid-template-columns: 300px 1fr;
  min-height: 100vh;
}

/* Sidebar */
#sidebar {
  background: var(--bg-panel);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  padding: 20px 0;
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
}
.brand {
  padding: 0 20px 20px;
  border-bottom: 1px solid var(--border);
  display: flex;
  gap: 12px;
  align-items: center;
}
.logo {
  width: 40px; height: 40px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  font-weight: 800; color: #fff;
}
.brand-title { font-weight: 700; }
.brand-sub { font-size: 12px; color: var(--fg-mute); }

.progress-summary {
  padding: 16px 20px;
  border-bottom: 1px solid var(--border);
}
.bar {
  height: 6px;
  background: var(--bg-elev);
  border-radius: 4px;
  overflow: hidden;
}
.bar-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--ok));
  width: 0%;
  transition: width 0.4s;
}
.bar-label {
  font-size: 12px;
  color: var(--fg-mute);
  margin-top: 8px;
}

#chapterNav {
  flex: 1;
  padding: 12px 8px;
  overflow-y: auto;
}
.nav-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  margin: 2px 0;
  border-radius: 8px;
  cursor: pointer;
  text-decoration: none;
  color: var(--fg);
  font-size: 14px;
  transition: background 0.15s;
}
.nav-item:hover { background: var(--bg-elev); }
.nav-item.active { background: var(--bg-elev); color: var(--accent); font-weight: 600; }
.nav-item .num {
  width: 24px; height: 24px;
  background: var(--bg-elev);
  border-radius: 6px;
  display: flex; align-items: center; justify-content: center;
  font-size: 11px;
  font-weight: 600;
  color: var(--fg-mute);
  flex-shrink: 0;
}
.nav-item.active .num { background: var(--accent); color: var(--bg); }
.nav-item.done .num { background: var(--ok); color: var(--bg); }
.nav-item.done .num::after { content: "✓"; font-size: 13px; }
.nav-item.done .num span { display: none; }
.nav-title { flex: 1; overflow: hidden; text-overflow: ellipsis; }

.sidebar-foot {
  padding: 12px 16px;
  border-top: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  gap: 8px;
}

/* Buttons */
button, .ghost {
  border: 1px solid var(--border);
  background: transparent;
  color: var(--fg);
  padding: 8px 14px;
  border-radius: 8px;
  font-size: 14px;
  cursor: pointer;
  font-family: inherit;
  text-decoration: none;
  display: inline-block;
  text-align: center;
  transition: all 0.15s;
}
button:hover, .ghost:hover { background: var(--bg-elev); border-color: var(--accent); }
.ghost.active { background: var(--bg-elev); border-color: var(--accent); color: var(--accent); font-weight: 600; }
.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  font-weight: 600;
}
.primary:hover { background: var(--accent); opacity: 0.9; color: #fff; }
.primary:disabled { opacity: 0.4; cursor: not-allowed; }

/* Main */
#main {
  display: flex;
  flex-direction: column;
  min-width: 0;
}
#topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 14px 32px;
  border-bottom: 1px solid var(--border);
  background: var(--bg-panel);
  position: sticky; top: 0; z-index: 10;
}
#crumbs { font-size: 13px; color: var(--fg-mute); }
.topbar-right { display: flex; gap: 8px; }

#content {
  padding: 32px 48px 64px;
  max-width: 880px;
  margin: 0 auto;
  width: 100%;
}
#content h1 { font-size: 32px; margin-top: 0; }
#content h2 { font-size: 22px; margin-top: 32px; padding-bottom: 6px; border-bottom: 1px solid var(--border); }
#content h3 { font-size: 17px; margin-top: 24px; color: var(--accent); }
#content p { margin: 12px 0; }
#content ul, #content ol { padding-left: 24px; }
#content li { margin: 6px 0; }
#content code {
  background: var(--code-bg);
  padding: 2px 6px;
  border-radius: 4px;
  font-family: "Cascadia Code", "Consolas", "Menlo", monospace;
  font-size: 13.5px;
}
#content pre {
  background: var(--code-bg);
  padding: 16px;
  border-radius: 8px;
  overflow-x: auto;
  border: 1px solid var(--border);
  margin: 16px 0;
}
#content pre code { background: transparent; padding: 0; font-size: 13px; }
#content blockquote {
  border-left: 3px solid var(--accent);
  padding: 8px 16px;
  margin: 16px 0;
  background: var(--bg-elev);
  border-radius: 0 8px 8px 0;
  color: var(--fg-mute);
}
#content table { width: 100%; border-collapse: collapse; margin: 16px 0; }
#content th, #content td {
  border: 1px solid var(--border);
  padding: 8px 12px;
  text-align: left;
}
#content th { background: var(--bg-elev); }

#chapterNav-foot {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  padding: 16px 48px;
  border-top: 1px solid var(--border);
  background: var(--bg-panel);
  position: sticky;
  bottom: 0;
}

/* Cards */
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 14px; margin: 20px 0; }
.card {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 16px;
  cursor: pointer;
  transition: all 0.15s;
  text-decoration: none;
  color: var(--fg);
  display: block;
}
.card:hover { border-color: var(--accent); transform: translateY(-2px); box-shadow: var(--shadow); }
.card .ch-num { font-size: 11px; color: var(--fg-mute); letter-spacing: 1px; text-transform: uppercase; }
.card .ch-title { font-weight: 600; margin: 4px 0 8px; font-size: 15px; }
.card .ch-desc { font-size: 13px; color: var(--fg-mute); }
.card.done { border-color: var(--ok); }
.card.done::after { content: "✓"; position: absolute; }
.card.locked { opacity: 0.5; cursor: not-allowed; }

/* Quiz */
.quiz {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px;
  margin: 24px 0;
}
.quiz h3 { margin-top: 0; color: var(--accent-2); }
.quiz-q { margin: 16px 0; }
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-opt {
  border: 1px solid var(--border);
  padding: 10px 14px;
  border-radius: 8px;
  cursor: pointer;
  background: var(--bg-elev);
  transition: all 0.15s;
}
.quiz-opt:hover { border-color: var(--accent); }
.quiz-opt.selected { border-color: var(--accent); background: rgba(108,182,255,0.1); }
.quiz-opt.correct { border-color: var(--ok); background: rgba(74,222,128,0.1); }
.quiz-opt.wrong { border-color: var(--err); background: rgba(248,113,113,0.1); }
.quiz-feedback {
  margin-top: 12px;
  padding: 12px;
  border-radius: 8px;
  font-size: 14px;
}
.quiz-feedback.ok { background: rgba(74,222,128,0.1); border: 1px solid var(--ok); }
.quiz-feedback.bad { background: rgba(248,113,113,0.1); border: 1px solid var(--err); }

/* Wizard */
.wizard {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 24px;
  margin: 20px 0;
}
.wizard-steps {
  display: flex;
  gap: 8px;
  margin-bottom: 24px;
}
.wizard-step {
  flex: 1;
  height: 4px;
  background: var(--bg-elev);
  border-radius: 2px;
}
.wizard-step.active { background: var(--accent); }
.wizard-step.done { background: var(--ok); }
.wizard textarea {
  width: 100%;
  min-height: 120px;
  background: var(--bg-elev);
  color: var(--fg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px;
  font-family: inherit;
  font-size: 14px;
  resize: vertical;
}
.wizard textarea:focus { outline: none; border-color: var(--accent); }
.wizard-nav { display: flex; justify-content: space-between; margin-top: 16px; }
.wizard-summary {
  background: var(--code-bg);
  padding: 16px;
  border-radius: 8px;
  border: 1px solid var(--border);
  white-space: pre-wrap;
  font-family: "Cascadia Code", "Consolas", monospace;
  font-size: 13px;
  margin-top: 16px;
}

/* Animator */
.animator {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px;
  margin: 24px 0;
}
.anim-row { display: flex; align-items: center; gap: 12px; margin: 12px 0; min-height: 48px; }
.anim-label { width: 110px; font-size: 13px; color: var(--fg-mute); }
.anim-track {
  flex: 1;
  background: var(--bg-elev);
  border-radius: 8px;
  height: 32px;
  position: relative;
  overflow: hidden;
}
.anim-bar {
  position: absolute;
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  border-radius: 8px;
  width: 0%;
  display: flex;
  align-items: center;
  padding: 0 12px;
  color: #fff;
  font-size: 12px;
  font-weight: 600;
  transition: width 0.1s linear;
  white-space: nowrap;
}
.anim-time { width: 80px; text-align: right; font-family: monospace; font-size: 13px; }
.anim-ctrls { display: flex; gap: 8px; margin-top: 16px; }

/* Callout */
.callout {
  border-left: 4px solid var(--accent);
  background: var(--bg-elev);
  padding: 12px 16px;
  margin: 16px 0;
  border-radius: 0 8px 8px 0;
}
.callout.warn { border-color: var(--warn); }
.callout.err { border-color: var(--err); }
.callout.ok { border-color: var(--ok); }
.callout-title { font-weight: 600; margin-bottom: 4px; font-size: 14px; }

/* Responsive */
@media (max-width: 900px) {
  #app { grid-template-columns: 1fr; }
  #sidebar { position: static; height: auto; }
  #content { padding: 24px 20px; }
  #chapterNav-foot { padding: 12px 20px; }
}