:root {
      --bg: #0f1220;
      --panel: #1a1f36;
      --panel-hover: #222867;
      --border: #2d3566;
      --text: #eaeaf0;
      --muted: #aab0d6;
      --accent: #2196f3; /* blue glow */
      --glow: rgba(33, 150, 243, 0.5);
    }

    * {
      box-sizing: border-box;
    }

    body {
      margin: 0;
      padding: 2rem;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
      background: linear-gradient(135deg, #0f1220, #141a3a);
      color: var(--text);
    }

    /* Navigation */
    ul {
      list-style: none;
      display: flex;
      gap: 0.8rem;
      padding: 0;
      margin-bottom: 1.5rem;
      flex-wrap: wrap;
    }

    ul li a {
      text-decoration: none;
      color: var(--text);
      background: var(--panel);
      padding: 0.6rem 1rem;
      border-radius: 12px;
      font-weight: 500;
      font-size: 0.95rem;
      transition: all 0.2s ease;
      box-shadow: 0 4px 8px rgba(0,0,0,0.25);
    }

    ul li a:hover {
      background: var(--panel-hover);
      color: var(--accent);
      transform: translateY(-2px);
      box-shadow: 0 8px 16px rgba(0,0,0,0.35);
    }

    /* Heading */
    h1 {
      text-align: center;
      font-size: 1.8rem;
      margin-bottom: 2rem;
      color: var(--accent);
      text-shadow: 0 2px 6px rgba(0,0,0,0.5);
    }

    /* Iframe styling with blue glow hover */
    #maintree {
      width: 100%;
      height: 70vh;
      border: 2px solid var(--border);
      border-radius: 12px;
      background: var(--panel);
      box-shadow: 0 10px 30px rgba(0,0,0,0.5);
      display: block;
      transition: transform 0.3s ease, box-shadow 0.3s ease;
    }

    #maintree:hover {
      transform: translateY(-5px);
      box-shadow: 0 20px 40px var(--glow), 0 10px 30px rgba(0,0,0,0.5);
    }

    /* Responsive */
    @media (max-width: 800px) {
      ul {
        flex-direction: column;
        gap: 0.5rem;
      }

      #maintree {
        height: 60vh;
      }
    }