:root {
      --bg: #20252b;
      --bg-alt: #2a3138;
      --header: #171b20;
      --text: #f5f5f5;
      --muted: #c4c7cc;
      --accent: #4fd36b;
    }

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

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
      background: var(--bg);
      color: var(--text);
      line-height: 1.4;
    }

    header {
      background: var(--header);
      padding: 14px 18px;
      text-align: center;
      position: sticky;
      top: 0;
      z-index: 10;
    }

    header h1 {
      font-size: 1.4rem;
    }

    main {
      max-width: 720px;
      margin: 20px auto 28px;
      padding: 0 14px;
    }

    .box {
      background: var(--bg-alt);
      padding: 16px 14px;
      border-radius: 10px;
      margin-bottom: 16px;
    }

    h2 {
      margin: 0 0 8px;
      font-size: 1.1rem;
    }

    p, li {
      font-size: 0.95rem;
      color: var(--muted);
    }

    a {
      color: var(--accent);
      text-decoration: none;
    }

    a:hover {
      text-decoration: underline;
    }

    code {
      background: #15181d;
      padding: 2px 5px;
      border-radius: 4px;
      font-size: 0.9rem;
    }

    ul, ol {
      padding-left: 18px;
      margin: 6px 0;
    }

    .btn-list {
      display: flex;
      flex-direction: column;
      gap: 10px;
      margin-top: 6px;
    }

    .link-btn {
      display: block;
      text-align: center;
      padding: 10px 12px;
      border-radius: 999px;
      background: #36404a;
      color: var(--text);
      font-size: 0.95rem;
    }

    .link-btn:hover {
      background: #424c57;
      text-decoration: none;
    }

    .link-btn span {
      display: inline-block;
      margin-right: 6px;
    }

    @media (min-width: 640px) {
      header h1 {
        font-size: 1.6rem;
      }

      .box {
        padding: 18px 16px;
      }

      p, li {
        font-size: 1rem;
      }

      .link-btn {
        font-size: 1rem;
      }
    }

    details summary {
      font-weight: 700;
      margin-top: 1rem;
    }