:root {
    --bg: #0b0f19;
    --card: #12182a;
    --text: #e7eaf3;
    --muted: #a7b0c3;
    --accent: #5aa9ff;
    --accent-2: #7bd389;
    --border: #1e2742;
  }
  
  * { box-sizing: border-box; }
  body {
    margin: 0;
    font-family: ui-sans-serif, system-ui, Segoe UI, Roboto, Arial, sans-serif;
    background: var(--bg);
    color: var(--text);
  }
  
  .container { max-width: 1200px; margin: 0 auto; padding: 0 16px; }
  
  .topbar {
    background: #0d1324;
    border-bottom: 1px solid var(--border);
    position: sticky; top: 0; z-index: 10;
  }
  .brand { margin: 0; font-size: 20px; }
  .brand a { color: var(--text); text-decoration: none; }
  
  .topbar .container {
    display: flex; align-items: center; gap: 24px; padding: 12px 16px;
  }
  .subjects a {
    color: var(--muted);
    margin-right: 12px;
    text-decoration: none;
    padding: 6px 10px;
    border-radius: 8px;
  }
  .subjects a.active, .subjects a:hover { background: var(--card); color: var(--text); }
  
  .main { display: grid; grid-template-columns: 260px 1fr; gap: 24px; padding: 24px 16px; }
  .sidebar { background: var(--card); border: 1px solid var(--border); padding: 16px; border-radius: 12px; }
  .sidebar-title { margin: 0 0 8px; font-size: 16px; color: var(--muted); }
  .topic-list { list-style: none; padding: 0; margin: 0; }
  .topic-list a {
    display: block; padding: 8px 10px; color: var(--text); text-decoration: none; border-radius: 8px;
  }
  .topic-list a.active, .topic-list a:hover { background: #0f162b; }
  
  .content { background: var(--card); border: 1px solid var(--border); padding: 24px; border-radius: 12px; }
  
  .footer { border-top: 1px solid var(--border); color: var(--muted); }
  .footer .container { padding: 16px; }
  
  /* Markdown styling */
  .md h1, .md h2, .md h3 { margin-top: 1.2em; }
  .md code { background: #0f162b; padding: 2px 6px; border-radius: 6px; }
  .md pre { background: #0f162b; padding: 12px; border-radius: 10px; overflow: auto; }
  .md table { border-collapse: collapse; width: 100%; }
  .md th, .md td { border: 1px solid var(--border); padding: 8px; }
  .md a { color: var(--accent); }