:root {
  --sidebar-width: 300px;
  --primary: #c0392b;
  --primary-dark: #922b21;
  --primary-light: #e74c3c;
  --bg: #faf8f5;
  --sidebar-bg: #1a1a2e;
  --sidebar-text: #e0e0e0;
  --sidebar-hover: #16213e;
  --text: #2c2c2c;
  --text-light: #666;
  --border: #e0ddd8;
  --accent: #e67e22;
  --card-bg: #fff;
}

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

body {
  font-family: 'Noto Sans SC', 'Noto Serif SC', 'Source Han Sans SC', 'Microsoft YaHei', sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.8;
  display: flex;
  min-height: 100vh;
}

/* Sidebar */
.sidebar {
  width: var(--sidebar-width);
  min-width: var(--sidebar-width);
  background: var(--sidebar-bg);
  color: var(--sidebar-text);
  height: 100vh;
  position: sticky;
  top: 0;
  overflow-y: auto;
  padding: 20px 0;
  z-index: 100;
  transition: transform 0.3s ease;
}

.sidebar-header {
  padding: 15px 20px;
  border-bottom: 1px solid rgba(255,255,255,0.1);
  text-align: center;
}

.sidebar-header h2 {
  font-size: 16px;
  color: #fff;
  margin-bottom: 4px;
  letter-spacing: 1px;
}

.sidebar-header .subtitle {
  font-size: 11px;
  color: rgba(255,255,255,0.5);
}

/* Mode switcher */
.mode-switcher {
  display: flex;
  margin: 10px 15px;
  border-radius: 6px;
  overflow: hidden;
  border: 1px solid rgba(255,255,255,0.2);
}

.mode-switcher a {
  flex: 1;
  padding: 6px 4px;
  text-align: center;
  font-size: 12px;
  color: rgba(255,255,255,0.7);
  text-decoration: none;
  transition: all 0.2s;
  background: transparent;
}

.mode-switcher a:hover {
  background: rgba(255,255,255,0.1);
  color: #fff;
}

.mode-switcher a.active {
  background: var(--primary);
  color: #fff;
}

/* TOC */
.toc {
  list-style: none;
  padding: 5px 0;
}

.toc-part {
  padding: 10px 20px 5px;
  font-size: 12px;
  color: var(--accent);
  font-weight: bold;
  text-transform: uppercase;
  letter-spacing: 1px;
}

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

.toc-item a {
  display: block;
  padding: 7px 20px 7px 30px;
  color: rgba(255,255,255,0.75);
  text-decoration: none;
  font-size: 13px;
  transition: all 0.15s;
  border-left: 3px solid transparent;
}

.toc-item a:hover {
  background: var(--sidebar-hover);
  color: #fff;
  border-left-color: var(--primary-light);
}

.toc-item a.active {
  background: rgba(192, 57, 43, 0.2);
  color: #fff;
  border-left-color: var(--primary-light);
}

.toc-special a {
  padding-left: 20px;
  font-weight: 500;
}

/* Main content */
.main-content {
  flex: 1;
  min-width: 0;
  display: flex;
  flex-direction: column;
}

.content-header {
  background: var(--card-bg);
  border-bottom: 1px solid var(--border);
  padding: 15px 30px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 50;
}

.content-header .breadcrumb {
  font-size: 13px;
  color: var(--text-light);
}

.content-header .breadcrumb a {
  color: var(--primary);
  text-decoration: none;
}

.content-header .breadcrumb a:hover {
  text-decoration: underline;
}

.nav-arrows {
  display: flex;
  gap: 10px;
}

.nav-arrows a {
  padding: 6px 14px;
  background: var(--sidebar-bg);
  color: #fff;
  text-decoration: none;
  border-radius: 4px;
  font-size: 13px;
  transition: background 0.2s;
}

.nav-arrows a:hover {
  background: var(--primary);
}

.content-body {
  max-width: 860px;
  margin: 0 auto;
  padding: 40px 30px 60px;
  width: 100%;
}

.content-body h1 {
  font-size: 28px;
  color: var(--primary-dark);
  margin-bottom: 30px;
  padding-bottom: 15px;
  border-bottom: 2px solid var(--primary);
}

.content-body h2 {
  font-size: 22px;
  color: var(--primary-dark);
  margin: 30px 0 15px;
}

.content-body h2.part-heading {
  font-size: 18px;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 2px;
  margin: 40px 0 20px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--accent);
}

.content-body h3 {
  font-size: 18px;
  color: var(--primary);
  margin: 25px 0 12px;
}

.content-body h4 {
  font-size: 16px;
  color: var(--text);
  margin: 20px 0 10px;
}

.content-body p {
  margin-bottom: 16px;
  text-align: justify;
  text-indent: 2em;
}

.content-body figure {
  margin: 25px 0;
  text-align: center;
}

.content-body figure img {
  max-width: 100%;
  height: auto;
  border-radius: 6px;
  box-shadow: 0 2px 12px rgba(0,0,0,0.1);
}

.content-body figure figcaption {
  font-size: 13px;
  color: var(--text-light);
  margin-top: 8px;
}

/* Bilingual mode */
.bilingual-container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 30px;
}

.bilingual-col {
  padding: 0 15px;
}

.bilingual-col:first-child {
  border-right: 1px solid var(--border);
}

.bilingual-col h2,
.bilingual-col h3,
.bilingual-col h4 {
  font-size: 0.9em;
}

.bilingual-label {
  display: inline-block;
  padding: 2px 8px;
  border-radius: 3px;
  font-size: 11px;
  margin-bottom: 10px;
  font-weight: bold;
}

.bilingual-label.cn {
  background: var(--primary);
  color: #fff;
}

.bilingual-label.en {
  background: var(--accent);
  color: #fff;
}

/* Mobile hamburger */
.hamburger {
  display: none;
  position: fixed;
  top: 15px;
  left: 15px;
  z-index: 200;
  background: var(--sidebar-bg);
  color: #fff;
  border: none;
  padding: 8px 12px;
  border-radius: 4px;
  cursor: pointer;
  font-size: 20px;
}

/* PDF download bar */
.pdf-download {
  background: linear-gradient(135deg, var(--primary-dark), var(--primary));
  color: #fff;
  padding: 12px 20px;
  text-align: center;
  font-size: 14px;
}

.pdf-download a {
  color: #fff;
  text-decoration: underline;
  margin: 0 15px;
  font-weight: 500;
}

.pdf-download a:hover {
  opacity: 0.9;
}

/* Cover page */
.cover-container {
  text-align: center;
  padding: 40px 20px;
}

.cover-container img {
  max-width: 350px;
  width: 100%;
  box-shadow: 0 4px 20px rgba(0,0,0,0.2);
  border-radius: 4px;
}

.cover-info {
  margin-top: 30px;
}

.cover-info h1 {
  font-size: 26px;
  border: none;
  margin-bottom: 10px;
}

.cover-info .authors {
  font-size: 16px;
  color: var(--text-light);
}

/* Responsive */
@media (max-width: 900px) {
  .bilingual-container {
    grid-template-columns: 1fr;
  }
  .bilingual-col:first-child {
    border-right: none;
    border-bottom: 1px solid var(--border);
    padding-bottom: 20px;
  }
}

@media (max-width: 768px) {
  .sidebar {
    position: fixed;
    left: 0;
    top: 0;
    transform: translateX(-100%);
  }
  .sidebar.open {
    transform: translateX(0);
  }
  .hamburger {
    display: block;
  }
  .content-body {
    padding: 30px 15px 40px;
  }
  .content-header {
    padding-left: 50px;
  }
}

/* Scrollbar */
.sidebar::-webkit-scrollbar {
  width: 4px;
}
.sidebar::-webkit-scrollbar-track {
  background: transparent;
}
.sidebar::-webkit-scrollbar-thumb {
  background: rgba(255,255,255,0.2);
  border-radius: 2px;
}