<details>
    <summary>Details</summary>
    Something small enough to escape casual notice.
</details>

    details {
            border: 1px solid #aaa;
            border-radius: 4px;
            padding: .5em .5em 0;
        }

        summary {
            font-weight: bold;
            margin: -.5em -.5em 0;
            padding: .5em;
        }

        details[open] {
            padding: .5em;
        }

        details[open] summary {
            border-bottom: 1px solid #aaa;
            margin-bottom: .5em;
        }