/* ===== CSS Variables ===== */
:root {
  --bg-color: #fafafa;
  --text-color: #333;
  --header-bg: #2c3e50;
  --header-text: #fff;
  --link-color: #3498db;
  --link-hover: #2980b9;
  --border-color: #ddd;
  --code-bg: #f4f4f4;
  --shadow: 0 2px 8px rgba(0,0,0,0.1);
  --nav-bg: #ecf0f1;
  --section-bg: #fff;
  --tag-bg: #3498db;
}

[data-theme="dark"] {
  --bg-color: #1a1a2e;
  --text-color: #e0e0e0;
  --header-bg: #16213e;
  --header-text: #fff;
  --link-color: #74b9ff;
  --link-hover: #0984e3;
  --border-color: #333;
  --code-bg: #2d2d44;
  --shadow: 0 2px 8px rgba(0,0,0,0.3);
  --nav-bg: #2d2d44;
  --section-bg: #16213e;
  --tag-bg: #74b9ff;
}

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

html {
  font-size: 18px;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background-color: var(--bg-color);
  color: var(--text-color);
  line-height: 1.8;
  min-height: 100vh;
  transition: background-color 0.3s, color 0.3s;
}

a {
  color: var(--link-color);
  text-decoration: none;
  transition: color 0.2s;
}

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

/* ===== Site Header ===== */
.site-header {
  background: var(--header-bg);
  color: var(--header-text);
  padding: 1.5rem 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow);
}

.site-header h1 {
  font-size: 1.5rem;
  font-weight: 600;
}

.theme-toggle {
  background: transparent;
  border: 2px solid var(--header-text);
  border-radius: 50%;
  width: 40px;
  height: 40px;
  cursor: pointer;
  font-size: 1.2rem;
  transition: transform 0.2s, background 0.2s;
}

.theme-toggle:hover {
  transform: scale(1.1);
  background: rgba(255,255,255,0.1);
}

/* ===== Main Content ===== */
.main-content {
  max-width: 900px;
  margin: 0 auto;
  padding: 2rem;
}

/* ===== Book Section ===== */
.book-section {
  background: var(--section-bg);
  border-radius: 12px;
  padding: 2rem;
  margin-bottom: 2rem;
  box-shadow: var(--shadow);
}

.section-title {
  font-size: 1.4rem;
  color: var(--header-bg);
  border-bottom: 2px solid var(--border-color);
  padding-bottom: 0.75rem;
  margin-bottom: 1.5rem;
}

[data-theme="dark"] .section-title {
  color: var(--link-color);
  border-bottom-color: var(--border-color);
}

.chapter-list {
  list-style: none;
}

.chapter-list li {
  padding: 0.75rem 0;
  border-bottom: 1px solid var(--border-color);
}

.chapter-list li:last-child {
  border-bottom: none;
}

.chapter-list a {
  display: block;
  padding: 0.5rem 0;
  font-size: 1.05rem;
}

.chapter-list a:hover {
  padding-left: 0.5rem;
}

/* ===== Site Footer ===== */
.site-footer {
  text-align: center;
  padding: 2rem;
  color: var(--text-color);
  opacity: 0.7;
  margin-top: 2rem;
}

/* ===== Chapter Page ===== */
.chapter-header {
  background: var(--header-bg);
  color: var(--header-text);
  padding: 1rem 2rem;
  display: flex;
  align-items: center;
  gap: 1rem;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow);
}

.back-link {
  color: var(--header-text);
  opacity: 0.9;
}

.back-link:hover {
  opacity: 1;
  color: var(--header-text);
}

.section-tag {
  background: var(--tag-bg);
  color: #fff;
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
  font-size: 0.85rem;
}

.tts-btn {
  background: transparent;
  border: 2px solid var(--header-text);
  border-radius: 50%;
  width: 36px;
  height: 36px;
  cursor: pointer;
  font-size: 1rem;
  transition: transform 0.2s, background 0.2s;
  margin-left: auto;
}

.tts-btn:hover {
  transform: scale(1.1);
  background: rgba(255,255,255,0.1);
}

.tts-player {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background: var(--header-bg);
  color: var(--header-text);
  padding: 0.75rem 1rem;
  display: flex;
  align-items: center;
  gap: 1rem;
  z-index: 200;
  box-shadow: 0 -2px 10px rgba(0,0,0,0.2);
}

.tts-play-btn {
  background: var(--tag-bg);
  border: none;
  border-radius: 50%;
  width: 40px;
  height: 40px;
  cursor: pointer;
  font-size: 1.2rem;
  color: #fff;
}

.tts-nav-btn {
  background: var(--nav-bg);
  border: none;
  border-radius: 50%;
  width: 36px;
  height: 36px;
  cursor: pointer;
  font-size: 1rem;
  color: var(--text-color);
}

.tts-status {
  flex: 1;
  font-size: 0.9rem;
}

.tts-close-btn {
  background: transparent;
  border: none;
  color: var(--header-text);
  font-size: 1.2rem;
  cursor: pointer;
  opacity: 0.7;
}

.tts-close-btn:hover {
  opacity: 1;
}

.chapter-container {
  max-width: 750px;
  margin: 0 auto;
  padding: 3rem 2rem;
}

.chapter-title {
  font-size: 1.8rem;
  text-align: center;
  margin-bottom: 2.5rem;
  color: var(--text-color);
}

.chapter-content p {
  margin-bottom: 1.5rem;
  text-align: justify;
  text-indent: 2em;
  transition: background-color 0.3s;
}

.chapter-content p.tts-highlight {
  background-color: #fff3cd;
  border-radius: 4px;
  padding: 0.5rem;
}

[data-theme="dark"] .chapter-content p.tts-highlight {
  background-color: #4a3f00;
}

/* ===== Chapter Navigation ===== */
.chapter-nav {
  max-width: 750px;
  margin: 0 auto;
  padding: 0 2rem 2rem;
  display: flex;
  justify-content: space-between;
  gap: 1rem;
}

.nav-btn {
  flex: 1;
  background: var(--nav-bg);
  color: var(--text-color);
  padding: 1rem;
  border-radius: 8px;
  text-align: center;
  font-size: 0.95rem;
  transition: transform 0.2s, box-shadow 0.2s;
}

.nav-btn:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
  color: var(--link-color);
}

.nav-btn.prev {
  text-align: left;
}

.nav-btn.next {
  text-align: right;
}

.chapter-footer {
  text-align: center;
  padding: 2rem;
  opacity: 0.7;
}

/* ===== Responsive ===== */
@media (max-width: 768px) {
  html {
    font-size: 16px;
  }

  .site-header {
    padding: 1rem 1.5rem;
  }

  .main-content {
    padding: 1rem;
  }

  .book-section {
    padding: 1.5rem;
  }

  .chapter-container {
    padding: 2rem 1rem;
  }

  .chapter-nav {
    flex-direction: column;
  }

  .nav-btn.prev,
  .nav-btn.next {
    text-align: center;
  }
}