details {
      margin: 1em 0;
      padding: 0.5em;
      border: 1px solid #ccc;
      border-radius: 5px;
      background-color: #fefefe;
      transition: all 0.3s ease;
    }

    summary {
      font-weight: bold;
      cursor: pointer;
      list-style: none;
    }

    summary::marker {
      content: "▶ ";
    }

    details[open] summary::marker {
      content: "▼ ";
    }

    details[open] {
      background-color: #f9f9f9;
    }