The details element represents a control from which the user can obtain additional information on-demand. It can be used to create an interactive widget that the user can show or hide (like expand and collapse) to retrieve the additional information or controls. Any sort of element can be placed inside the details element.
For further reading:
W3schools: https://www.w3schools.com/tags/tag_details.asp
Tutorial republic: https://www.tutorialrepublic.com/html-reference/html5-details-tag.php
HTML all tutorials: https://www.youtube.com/watch?v=rRDw0PMAs6s&list=PLaHzrTVniWQWD3a23a7NZPVtZPKPKvQsi
CSS all tutorials: https://www.youtube.com/watch?v=s3rYM8_JqUo&list=PLaHzrTVniWQV8wIMXEx7Y-5RZ6gt7n1bN