:root {
  --bg: #f4efe6;
  --paper: #fffaf2;
  --paper-strong: #fffdf8;
  --ink: #2e241c;
  --muted: #7d6b5d;
  --accent: #b45a3c;
  --accent-soft: #e9c7b2;
  --line: rgba(92, 68, 50, 0.14);
  --shadow: 0 22px 55px rgba(79, 52, 33, 0.15);
}

body.dark {
  --bg: #1d1b1a;
  --paper: #26211f;
  --paper-strong: #2e2725;
  --ink: #f4eadf;
  --muted: #c8b6a7;
  --accent: #f08c62;
  --accent-soft: #58392f;
  --line: rgba(255, 234, 220, 0.12);
  --shadow: 0 22px 55px rgba(0, 0, 0, 0.32);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  color: var(--ink);
  font-family: "Noto Serif TC", "PMingLiU", serif;
  background:
    radial-gradient(circle at top left, rgba(255, 255, 255, 0.65), transparent 30%),
    linear-gradient(135deg, #e5d4c0, var(--bg));
  transition: background 0.25s ease, color 0.25s ease;
}

body.dark {
  background:
    radial-gradient(circle at top left, rgba(240, 140, 98, 0.12), transparent 30%),
    linear-gradient(135deg, #151413, var(--bg));
}

.app-shell {
  display: grid;
  grid-template-columns: 320px 1fr;
  gap: 24px;
  max-width: 1400px;
  margin: 0 auto;
  padding: 24px;
}

.sidebar,
.reader {
  background: rgba(255, 255, 255, 0.28);
  backdrop-filter: blur(12px);
  border: 1px solid var(--line);
  border-radius: 24px;
  box-shadow: var(--shadow);
}

.sidebar {
  padding: 24px;
}

.brand h1,
.reader-header h2 {
  margin: 0;
  text-decoration: none;
}

.eyebrow,
.subtitle,
.chapter-kicker,
#progress-text,
#chapter-count {
  color: var(--muted);
  text-decoration: none;
}

.brand,
.brand p,
.brand h1 {
  text-decoration: none !important;
  box-shadow: none;
}

.eyebrow {
  margin: 0 0 8px;
  font-size: 0.8rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
}

.subtitle {
  margin-top: 10px;
  line-height: 1.7;
}

.intro-panel p,
.site-note p {
  margin: 0;
  line-height: 1.8;
}

.site-highlights {
  margin: 16px 0 0;
  padding-left: 1.4em;
  line-height: 1.8;
}

.site-highlights li {
  margin-bottom: 8px;
}

.site-highlights li:last-child {
  margin-bottom: 0;
}

.site-note-compact {
  margin-top: 12px !important;
  color: var(--muted);
}

.panel {
  margin-top: 24px;
  padding-top: 20px;
  border-top: 1px solid var(--line);
}

.panel-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.panel h2 {
  margin: 0;
  font-size: 1rem;
}

.about-links {
  display: grid;
  gap: 12px;
}

.about-links a {
  display: block;
  padding: 12px 14px;
  color: var(--ink);
  text-decoration: none;
  background: rgba(255, 255, 255, 0.38);
  border: 1px solid transparent;
  border-radius: 14px;
  transition: transform 0.18s ease, background 0.18s ease, border-color 0.18s ease;
}

.about-links a:hover {
  background: var(--paper);
  border-color: var(--accent-soft);
  transform: translateX(4px);
}

.toc {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-top: 18px;
}

.toc button,
.reader-footer button,
.controls button {
  border: 0;
  border-radius: 14px;
  cursor: pointer;
  transition: transform 0.18s ease, background 0.18s ease, color 0.18s ease;
}

.toc button {
  width: 100%;
  padding: 14px 16px;
  text-align: left;
  color: var(--ink);
  background: rgba(255, 255, 255, 0.38);
  border: 1px solid transparent;
}

.toc button:hover,
.toc button.active {
  background: var(--paper);
  border-color: var(--accent-soft);
  transform: translateX(4px);
}

.font-controls {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin: 18px 0 12px;
}

.font-controls button,
.secondary,
.reader-footer button {
  padding: 12px 16px;
  color: var(--ink);
  background: var(--paper);
}

.secondary {
  width: 100%;
}

.reader {
  display: flex;
  flex-direction: column;
  min-height: calc(100vh - 48px);
  padding: 32px;
}

.reader-header,
.reader-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
}

.chapter-kicker {
  margin: 0 0 8px;
}

.progress-wrap {
  min-width: 220px;
}

.progress-bar {
  width: 100%;
  height: 10px;
  margin-top: 10px;
  overflow: hidden;
  background: rgba(255, 255, 255, 0.45);
  border-radius: 999px;
}

#progress-bar-fill {
  width: 0%;
  height: 100%;
  background: linear-gradient(90deg, var(--accent), #f0bc8d);
  border-radius: inherit;
}

.chapter-content {
  flex: 1;
  margin: 28px 0;
  padding: 40px;
  font-size: 18px;
  line-height: 2;
  background: linear-gradient(180deg, var(--paper-strong), var(--paper));
  border: 1px solid var(--line);
  border-radius: 24px;
  overflow-wrap: break-word;
}

.chapter-content p {
  margin: 0 0 1.4em;
  text-indent: 2em;
}

.example-block,
.pitfall-block,
.summary-block,
.task-block,
.cheatsheet-block,
.exercise-block {
  margin-top: 42px;
  padding-top: 28px;
  border-top: 1px solid var(--line);
}

.example-block h3,
.pitfall-block h3,
.summary-block h3,
.task-block h3,
.cheatsheet-block h3,
.exercise-block h3 {
  margin: 0 0 16px;
  font-size: 1.15rem;
}

.example-list {
  display: grid;
  gap: 16px;
}

.example-card {
  padding: 18px 20px;
  background: rgba(255, 255, 255, 0.42);
  border: 1px solid var(--line);
  border-radius: 18px;
}

.example-card h4 {
  margin: 0 0 12px;
  font-size: 1rem;
}

.example-card pre {
  margin: 0 0 12px;
  padding: 14px 16px;
  overflow-x: auto;
  color: #f7efe7;
  background: #2c241f;
  border-radius: 14px;
}

.example-card code {
  font-family: Consolas, "Courier New", monospace;
}

.example-card p {
  margin: 0;
  text-indent: 0;
}

.example-output-wrap {
  margin-bottom: 12px;
}

.example-output-wrap .label {
  margin: 0 0 8px;
  font-weight: 700;
  text-indent: 0;
}

.pitfall-list {
  display: grid;
  gap: 16px;
}

.pitfall-card,
.summary-list {
  padding: 18px 20px;
  background: rgba(255, 255, 255, 0.38);
  border: 1px solid var(--line);
  border-radius: 18px;
}

.pitfall-card p {
  margin: 0 0 10px;
  text-indent: 0;
}

.pitfall-card p:last-child {
  margin-bottom: 0;
}

.pitfall-problem {
  color: var(--ink);
}

.summary-list {
  margin: 0;
  padding-left: 2em;
}

.summary-list li {
  margin-bottom: 10px;
  line-height: 1.9;
}

.summary-list li:last-child {
  margin-bottom: 0;
}

.quiz-list,
.cheatsheet-list {
  display: grid;
  gap: 16px;
}

.quiz-card,
.cheatsheet-card,
.task-list {
  padding: 18px 20px;
  background: rgba(255, 255, 255, 0.4);
  border: 1px solid var(--line);
  border-radius: 18px;
}

.exercise-group + .exercise-group {
  margin-top: 28px;
}

.exercise-group-title {
  margin: 0 0 14px;
  font-size: 1rem;
}

.quiz-card h5,
.exercise-card h5 {
  margin: 0 0 10px;
  font-size: 1rem;
}

.quiz-question,
.quiz-answer,
.cheatsheet-card p {
  text-indent: 0;
}

.quiz-question {
  margin: 0 0 10px;
  font-weight: 700;
}

.quiz-options {
  margin: 0 0 12px;
  padding-left: 1.5em;
}

.quiz-options li {
  margin-bottom: 8px;
}

.option-label {
  display: inline-block;
  min-width: 1.6em;
  font-weight: 700;
}

.quiz-answer {
  margin: 0;
  padding: 10px 12px;
  background: rgba(180, 90, 60, 0.1);
  border: 1px solid rgba(180, 90, 60, 0.18);
  border-radius: 12px;
}

.task-list {
  margin: 0;
  padding-left: 2em;
}

.task-list li {
  margin-bottom: 10px;
  line-height: 1.9;
}

.task-list li:last-child {
  margin-bottom: 0;
}

.cheatsheet-command {
  margin: 0 0 8px;
  font-weight: 700;
}

.cheatsheet-example {
  margin-top: 10px;
  text-indent: 0;
}

.cheatsheet-example code {
  font-family: Consolas, "Courier New", monospace;
}

.cheatsheet-card p:last-child {
  margin-bottom: 0;
}

.appendix-only {
  margin-top: 0;
  padding-top: 0;
  border-top: 0;
}

.exercise-list {
  margin: 0;
  display: grid;
  gap: 16px;
}

.exercise-card {
  padding: 18px 20px;
  background: rgba(255, 255, 255, 0.4);
  border: 1px solid var(--line);
  border-radius: 18px;
}

.exercise-card h4 {
  margin: 0 0 10px;
  font-size: 1rem;
}

.exercise-card p {
  margin: 0 0 10px;
  text-indent: 0;
}

.exercise-card p:last-child {
  margin-bottom: 0;
}

.exercise-question {
  font-weight: 700;
}

.exercise-explanation {
  color: var(--muted);
}

.reader-footer {
  justify-content: flex-end;
}

.reader-footer button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

@media (max-width: 960px) {
  .app-shell {
    grid-template-columns: 1fr;
  }

  .reader {
    min-height: auto;
  }
}

@media (max-width: 640px) {
  .app-shell,
  .sidebar,
  .reader {
    padding: 16px;
  }

  .reader-header,
  .reader-footer {
    flex-direction: column;
    align-items: stretch;
  }

  .chapter-content {
    padding: 24px 18px;
  }
}