:root {
  --bg-primary: #f5f5f5;
  --bg-secondary: #ffffff;
  --text-primary: #333333;
  --text-secondary: #666666;
  --accent-color: #4a90d9;
  --border-color: #e0e0e0;
  --font-size-base: 18px;
  --line-height: 1.8;
}

[data-theme="dark"] {
  --bg-primary: #1a1a1a;
  --bg-secondary: #252525;
  --text-primary: #e0e0e0;
  --text-secondary: #a0a0a0;
  --border-color: #3a3a3a;
}

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

body {
  font-family: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Segoe UI", sans-serif;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-size: var(--font-size-base);
  line-height: var(--line-height);
  transition: background-color 0.3s, color 0.3s;
  min-height: 100vh;
}

a {
  color: inherit;
  text-decoration: none;
}

.header {
  position: sticky;
  top: 0;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-color);
  padding: 0 30px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  z-index: 100;
}

.header-left {
  display: flex;
  align-items: center;
  gap: 20px;
}

.site-title {
  font-size: 1.2em;
  font-weight: 600;
  padding: 15px 0;
}

.book-title {
  font-size: 1.1em;
  font-weight: 600;
  padding: 12px 0;
}

.header-right {
  display: flex;
  align-items: center;
  gap: 20px;
}

.toolbar-btn {
  background: none;
  border: 1px solid var(--border-color);
  padding: 8px 16px;
  border-radius: 6px;
  cursor: pointer;
  color: var(--text-primary);
  font-size: 0.9em;
  display: flex;
  align-items: center;
  gap: 6px;
  transition: all 0.2s;
}

.toolbar-btn:hover {
  border-color: var(--accent-color);
  color: var(--accent-color);
}

.font-controls {
  display: flex;
  align-items: center;
  gap: 8px;
}

.font-btn {
  width: 32px;
  height: 32px;
  border: 1px solid var(--border-color);
  background: var(--bg-secondary);
  border-radius: 4px;
  cursor: pointer;
  color: var(--text-primary);
  font-size: 1.1em;
  transition: all 0.2s;
}

.font-btn:hover {
  border-color: var(--accent-color);
  color: var(--accent-color);
}

.main {
  max-width: 900px;
  margin: 0 auto;
  padding: 40px 30px 80px;
}

.page-title {
  font-size: 1.5em;
  margin-bottom: 30px;
  padding-bottom: 15px;
  border-bottom: 2px solid var(--border-color);
}

.book-list {
  display: grid;
  gap: 20px;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
}

.book-card {
  display: block;
  padding: 25px;
  background: var(--bg-secondary);
  border-radius: 12px;
  border: 1px solid var(--border-color);
  transition: all 0.2s;
}

.book-card:hover {
  border-color: var(--accent-color);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

.book-card-title {
  font-size: 1.2em;
  font-weight: 600;
  margin-bottom: 8px;
  color: var(--accent-color);
}

.book-card-author {
  font-size: 0.9em;
  color: var(--text-secondary);
  margin-bottom: 12px;
}

.book-card-meta {
  font-size: 0.85em;
  color: var(--text-secondary);
}

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

.toc-item {
  display: block;
  padding: 15px 20px;
  margin: 5px 0;
  background: var(--bg-secondary);
  border-radius: 8px;
  transition: all 0.2s;
  border: 1px solid transparent;
}

.toc-item:hover {
  border-color: var(--accent-color);
  transform: translateX(5px);
}

.toc-item-number {
  color: var(--accent-color);
  font-weight: 600;
  margin-right: 10px;
}

.chapter-title {
  font-size: 1.6em;
  font-weight: 600;
  margin-bottom: 30px;
  padding-bottom: 15px;
  border-bottom: 2px solid var(--border-color);
}

.chapter-content {
  text-align: justify;
  text-indent: 2em;
}

.chapter-content p {
  margin-bottom: 1em;
}

.navigation {
  display: flex;
  justify-content: space-between;
  margin-top: 60px;
  padding-top: 30px;
  border-top: 1px solid var(--border-color);
}

.nav-link {
  display: flex;
  flex-direction: column;
  padding: 15px 25px;
  background: var(--bg-secondary);
  border-radius: 8px;
  border: 1px solid var(--border-color);
  transition: all 0.2s;
  min-width: 140px;
}

.nav-link:hover {
  border-color: var(--accent-color);
}

.nav-link.disabled {
  opacity: 0.4;
  pointer-events: none;
}

.nav-label {
  font-size: 0.85em;
  color: var(--text-secondary);
  margin-bottom: 5px;
}

.nav-text {
  font-weight: 500;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.nav-link.next {
  text-align: right;
  margin-left: auto;
}

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  margin-bottom: 20px;
  color: var(--accent-color);
  font-size: 0.9em;
}

.back-link:hover {
  text-decoration: underline;
}

.progress-bar {
  position: fixed;
  top: 57px;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--border-color);
  z-index: 99;
}

.progress-fill {
  height: 100%;
  background: var(--accent-color);
  width: 0%;
  transition: width 0.1s;
}

@media (max-width: 768px) {
  .header {
    padding: 0 15px;
    flex-wrap: wrap;
    gap: 10px;
  }
  
  .header-right {
    gap: 10px;
  }
  
  .toolbar-btn span {
    display: none;
  }
  
  .main {
    padding: 30px 15px 80px;
  }
  
  .book-list {
    grid-template-columns: 1fr;
  }
  
  .navigation {
    flex-direction: column;
    gap: 10px;
  }
  
  .nav-link {
    width: 100%;
  }
  
  .nav-link.next {
    text-align: left;
    margin-left: 0;
  }
}