:root {
  --bg: #0f172a;
  --panel: #111827;
  --panel-2: #1f2937;
  --text: #e5e7eb;
  --muted: #94a3b8;
  --accent: #22c55e;
  --border: #334155;
  --code-bg: #0b1220;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  color: var(--text);
  background: linear-gradient(135deg, #020617, #0f172a 45%, #111827);
  font-family: "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
}

.topbar {
  padding: 20px 24px 14px;
  border-bottom: 1px solid var(--border);
  background: rgba(17, 24, 39, 0.78);
  backdrop-filter: blur(8px);
}

.topbar h1 {
  margin: 0;
  font-size: 24px;
}

.topbar p {
  margin: 8px 0 0;
  color: var(--muted);
  font-size: 14px;
}

.layout {
  display: grid;
  grid-template-columns: 300px 1fr;
  min-height: calc(100vh - 90px);
}

.sidebar {
  border-right: 1px solid var(--border);
  background: rgba(2, 6, 23, 0.45);
  padding: 14px;
  position: sticky;
  top: 0;
  height: calc(100vh - 90px);
  overflow: auto;
}

.sidebar-head {
  display: flex;
  align-items: center;
  justify-content: flex-start;
  gap: 10px;
}

.sidebar h2 {
  font-size: 16px;
  margin: 0;
}

.chapter-nav {
  margin-top: 12px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.chapter-btn {
  text-align: left;
  border: 1px solid var(--border);
  background: var(--panel);
  color: var(--text);
  border-radius: 10px;
  padding: 10px 12px;
  cursor: pointer;
  font-size: 13px;
  line-height: 1.35;
}

.chapter-btn:hover {
  border-color: #475569;
}

.chapter-btn.active {
  border-color: var(--accent);
  box-shadow: 0 0 0 1px rgba(34, 197, 94, 0.35) inset;
}

.content-wrap {
  padding: 22px;
}

.content {
  max-width: 980px;
  margin: 0 auto;
  background: rgba(17, 24, 39, 0.72);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 22px 24px 28px;
}

.loading {
  color: var(--muted);
}

.content h1,
.content h2,
.content h3 {
  scroll-margin-top: 12px;
}

.content p,
.content li,
.content blockquote {
  line-height: 1.72;
}

.content a {
  color: #7dd3fc;
}

.content table {
  border-collapse: collapse;
  width: 100%;
  margin: 14px 0;
  overflow: auto;
  display: block;
}

.content th,
.content td {
  border: 1px solid #475569;
  padding: 8px 10px;
}

.content pre {
  background: var(--code-bg);
  border: 1px solid #334155;
  border-radius: 10px;
  padding: 12px 14px;
  overflow: auto;
}

.content pre.code-block {
  position: relative;
  border: 1px solid #475569;
  box-shadow: 0 0 0 1px rgba(125, 211, 252, 0.12) inset;
  padding-top: 34px;
}

.content pre.code-block::before {
  content: attr(data-lang);
  position: absolute;
  top: 8px;
  right: 10px;
  font-size: 11px;
  line-height: 1;
  letter-spacing: 0.08em;
  color: #cbd5e1;
  background: rgba(15, 23, 42, 0.9);
  border: 1px solid #475569;
  border-radius: 999px;
  padding: 4px 8px;
}

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

.content blockquote {
  margin: 0;
  padding: 8px 14px;
  border-left: 4px solid #334155;
  background: rgba(15, 23, 42, 0.55);
}

@media (max-width: 980px) {
  .layout {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
    height: auto;
    border-right: 0;
    border-bottom: 1px solid var(--border);
  }
}