:root {
  --bg-color: #ffffff;
  --text-color: #24292f;
  --muted-color: #57606a;
  --border-color: #d0d7de;
  --link-color: #0969da;
  --hover-bg: #f6f8fa;
  --sidebar-bg: #f6f8fa;
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji";
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
  --container-width: 1200px;
}

[data-theme="dark"] {
  --bg-color: #0d1117;
  --text-color: #c9d1d9;
  --muted-color: #8b949e;
  --border-color: #30363d;
  --link-color: #58a6ff;
  --hover-bg: #161b22;
  --sidebar-bg: #010409;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  padding: 0;
  font-family: var(--font-sans);
  background-color: var(--bg-color);
  color: var(--text-color);
  line-height: 1.5;
}

/* Layout */
.app-container {
  display: flex;
  min-height: 100vh;
}

.sidebar {
  width: 280px;
  background-color: var(--sidebar-bg);
  border-right: 1px solid var(--border-color);
  padding: 24px;
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
}

.main-content {
  flex: 1;
  padding: 40px 60px;
  max-width: var(--container-width);
}

/* Sidebar Nav */
.brand {
  margin-bottom: 32px;
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text-color);
}

.brand-logo { width: 32px; height: 32px; }
.brand-name { font-weight: 600; font-size: 1.25rem; }

.nav-group-title {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--muted-color);
  text-transform: uppercase;
  margin-bottom: 8px;
  margin-top: 24px;
}

.nav-link {
  display: block;
  padding: 6px 12px;
  border-radius: 6px;
  color: var(--text-color);
  text-decoration: none;
  font-size: 0.875rem;
  transition: background 0.2s;
}

.nav-link:hover { background: var(--hover-bg); }
.nav-link.active { background: var(--hover-bg); font-weight: 600; color: var(--link-color); }

/* Markdown Content */
.markdown-body h1 { font-size: 2rem; margin-top: 0; padding-bottom: 0.3em; border-bottom: 1px solid var(--border-color); }
.markdown-body h2 { font-size: 1.5rem; margin-top: 24px; border-bottom: 1px solid var(--border-color); padding-bottom: 0.3em; }
.markdown-body p { margin-top: 16px; margin-bottom: 16px; }
.markdown-body a { color: var(--link-color); text-decoration: none; }
.markdown-body a:hover { text-decoration: underline; }
.markdown-body pre { background: var(--hover-bg); padding: 16px; border-radius: 6px; overflow: auto; }
.markdown-body code { font-family: var(--font-mono); font-size: 85%; background: rgba(175, 184, 193, 0.2); padding: 0.2em 0.4em; border-radius: 6px; }
.markdown-body img { max-width: 100%; border-radius: 6px; border: 1px solid var(--border-color); }

/* Theme Toggle */
.theme-toggle-btn {
  margin-top: auto;
  padding: 8px 16px;
  background: transparent;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  color: var(--text-color);
  cursor: pointer;
  font-size: 0.875rem;
}

@media (max-width: 768px) {
  .app-container { flex-direction: column; }
  .sidebar { width: 100%; height: auto; position: static; }
  .main-content { padding: 24px; }
}