The details element allows you to create an expandable block that is hidden by default. Sometimes this element is also called accordion.
This element contains a summary element that represents the title for the block, and this title is displayed in hidden mode. For example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>List In HTML5</title>
</head>
<body>
<h1>The details and summary elements with internal CSS</h1>
<details>
<summary>Top Cars</summary>
<ul style="list-style-type:upper-roman;">
<li>Volkswagen Plus</li>
<li>Ford Motor Edge</li>
<li>Nexus 6P</li>
<li>Toyota XL</li>
</ul>
</details>
</body>
</html>
By default, we only see the summary header.
By clicking on the arrow or heading, we can expand the block:
