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

:root {
  --bg-primary: #1e1e1e;
  --bg-secondary: #252526;
  --bg-tertiary: #2d2d2d;
  --bg-hover: #37373d;
  --bg-active: #094771;
  --border: #3c3c3c;
  --text-primary: #cccccc;
  --text-secondary: #969696;
  --text-muted: #6a6a6a;
  --accent: #0078d4;
  --accent-hover: #1a8adf;
  --tag-bg: #2a2d2e;
  --tag-text: #75beff;
  --scrollbar-bg: #1e1e1e;
  --scrollbar-thumb: #424242;
  --scrollbar-hover: #4f4f4f;
}

html, body {
  height: 100%;
  font-family: 'Segoe UI', -apple-system, BlinkMacSystemFont, sans-serif;
  font-size: 13px;
  color: var(--text-primary);
  background: var(--bg-primary);
}

#app {
  display: flex;
  height: 100vh;
  overflow: hidden;
}

::-webkit-scrollbar {
  width: 8px;
}

::-webkit-scrollbar-track {
  background: var(--scrollbar-bg);
}

::-webkit-scrollbar-thumb {
  background: var(--scrollbar-thumb);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--scrollbar-hover);
}

#sidebar {
  width: 280px;
  min-width: 280px;
  background: var(--bg-secondary);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

#sidebar-header {
  padding: 16px 14px 12px;
  border-bottom: 1px solid var(--border);
}

#sidebar-header h1 {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: var(--text-secondary);
  margin-bottom: 10px;
}

#search {
  width: 100%;
  padding: 5px 8px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  border-radius: 4px;
  color: var(--text-primary);
  font-size: 12px;
  font-family: inherit;
  outline: none;
  transition: border-color 0.15s;
}

#search:focus {
  border-color: var(--accent);
}

#search::placeholder {
  color: var(--text-muted);
}

#book-list {
  flex: 1;
  overflow-y: auto;
  padding: 8px 0;
}

.tag-group {
  margin-bottom: 4px;
}

.tag-group-header {
  padding: 4px 14px;
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  color: var(--text-muted);
  cursor: pointer;
  user-select: none;
  display: flex;
  align-items: center;
  gap: 4px;
}

.tag-group-header:hover {
  color: var(--text-secondary);
}

.tag-group-header .chevron {
  font-size: 10px;
  transition: transform 0.15s;
  display: inline-block;
}

.tag-group-header .chevron.collapsed {
  transform: rotate(-90deg);
}

.tag-group-items {
  overflow: hidden;
}

.tag-group-items.collapsed {
  display: none;
}

.book-item {
  padding: 6px 14px 6px 24px;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-primary);
  font-size: 13px;
  transition: background-color 0.1s;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.book-item:hover {
  background: var(--bg-hover);
}

.book-item.active {
  background: var(--bg-active);
}

.book-item .book-icon {
  color: var(--text-muted);
  font-size: 14px;
  flex-shrink: 0;
}

.book-item .book-name {
  overflow: hidden;
  text-overflow: ellipsis;
}

#content {
  flex: 1;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  background: var(--bg-primary);
}

#empty-state {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  color: var(--text-muted);
  gap: 12px;
}

#empty-icon {
  font-size: 48px;
  opacity: 0.3;
}

#empty-state p {
  font-size: 14px;
}

#book-view {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

#book-view.hidden {
  display: none;
}

#book-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 20px;
  border-bottom: 1px solid var(--border);
  background: var(--bg-secondary);
}

#book-title {
  font-size: 14px;
  font-weight: 600;
  color: var(--text-primary);
}

#book-tags {
  display: inline-flex;
  gap: 6px;
  margin-top: 4px;
}

#book-tags .tag {
  font-size: 11px;
  padding: 1px 6px;
  background: var(--tag-bg);
  color: var(--tag-text);
  border-radius: 3px;
}

#open-tab {
  padding: 5px 12px;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 4px;
  font-size: 12px;
  font-family: inherit;
  cursor: pointer;
  white-space: nowrap;
  transition: background-color 0.15s;
}

#open-tab:hover {
  background: var(--accent-hover);
}

#chapter-nav {
  display: flex;
  gap: 0;
  padding: 0 20px;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  overflow-x: auto;
}

.chapter-tab {
  padding: 8px 16px;
  font-size: 12px;
  color: var(--text-secondary);
  cursor: pointer;
  border-bottom: 2px solid transparent;
  white-space: nowrap;
  transition: color 0.15s, border-color 0.15s;
}

.chapter-tab:hover {
  color: var(--text-primary);
}

.chapter-tab.active {
  color: var(--text-primary);
  border-bottom-color: var(--accent);
}

#chapter-content {
  flex: 1;
  overflow-y: auto;
  padding: 24px 32px;
  line-height: 1.6;
}

#chapter-content h1,
#chapter-content h2,
#chapter-content h3,
#chapter-content h4 {
  color: #e0e0e0;
  margin: 1.2em 0 0.5em;
}

#chapter-content h1 { font-size: 1.8em; }
#chapter-content h2 { font-size: 1.4em; }
#chapter-content h3 { font-size: 1.15em; }

#chapter-content p {
  margin: 0.6em 0;
}

#chapter-content a {
  color: var(--tag-text);
  text-decoration: underline;
}

#chapter-content a:hover {
  color: #a8d4ff;
}

#chapter-content code {
  font-family: 'Cascadia Code', 'Fira Code', 'Consolas', monospace;
  background: var(--bg-tertiary);
  padding: 2px 5px;
  border-radius: 3px;
  font-size: 0.9em;
}

#chapter-content pre {
  background: #0a0a0a;
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 14px 16px;
  overflow-x: auto;
  margin: 1em 0;
  position: relative;
}

#chapter-content pre code {
  background: none;
  padding: 0;
  color: #4ec9b0;
}

#chapter-content pre .copy-btn {
  position: absolute;
  top: 6px;
  right: 6px;
  background: #3c3c3c;
  color: #969696;
  border: none;
  border-radius: 3px;
  padding: 3px 8px;
  font-size: 11px;
  font-family: inherit;
  cursor: pointer;
  opacity: 0;
  transition: opacity 0.15s;
}

#chapter-content pre:hover .copy-btn {
  opacity: 1;
}

#chapter-content pre .copy-btn:hover {
  background: #4f4f4f;
  color: #cccccc;
}

#chapter-content .click-instruction {
  color: #e89b5e;
  font-style: italic;
}

#chapter-content .warning-box {
  border-left: 3px solid #e8975e;
  background: rgba(232, 155, 94, 0.08);
  padding: 10px 16px;
  margin: 1em 0;
  border-radius: 0 4px 4px 0;
}

#chapter-content .info-box {
  border-left: 3px solid var(--accent);
  background: rgba(0, 120, 212, 0.08);
  padding: 10px 16px;
  margin: 1em 0;
  border-radius: 0 4px 4px 0;
}

#chapter-content img {
  max-width: 100%;
  border-radius: 4px;
  margin: 0.8em 0;
}

#chapter-content table {
  border-collapse: collapse;
  width: 100%;
  margin: 1em 0;
}

#chapter-content th,
#chapter-content td {
  border: 1px solid var(--border);
  padding: 8px 12px;
  text-align: left;
}

#chapter-content th {
  background: var(--bg-secondary);
  font-weight: 600;
}

#chapter-content blockquote {
  border-left: 3px solid var(--accent);
  margin: 1em 0;
  padding: 8px 16px;
  color: var(--text-secondary);
  background: var(--bg-secondary);
  border-radius: 0 4px 4px 0;
}

#chapter-content ul,
#chapter-content ol {
  padding-left: 24px;
  margin: 0.6em 0;
}

.search-highlight {
  background: rgba(255, 213, 0, 0.25);
  color: #ffd500;
  border-radius: 2px;
  padding: 0 2px;
}

@media (max-width: 768px) {
  #sidebar {
    width: 220px;
    min-width: 220px;
  }

  #chapter-content {
    padding: 16px;
  }
}