<details>
HTML element
Click below to see the code which creates this kinda dropdown, it is the <details>
element.
A <details> code example (click here)
<details> <summary>A <details> code example (click here)</summary> ... too much recursion ... ;) </details>
The <details>
element "creates a disclosure widget in which information is visible only when the widget is toggled into an "open" state" MDN says.