The <details> tag contains additional details, that the user can open and view. By default, the content of the tag is not shown. In order to display the contents, you must apply the open attribute.
The <summary> sets the visible title, which, when clicked, will open/close additional information. If there is no header, then by default the browser will show the header "More details".
The <details> tag comes in pairs, the content is written between the opening (<details>) and the closing (</details>) tags.
<html> <head> <title>Title of the document</title> </head> <body> <details> <summary>Click to see details</summary> <p>Detailed information is here.</p> </details> </body> </html>
|open||open||Indicates that the information in the tag should initially be shown in expanded form.|