Hi,

Here is an example of adding drop-down list in the header:
https://codepen.io/svetoslavb04/pen/MWzNpvq

As you can see, you should use a header template to set the content of the header.
Next, the drop-down of the list should be appended to the body in order to open properly.

Best Regards,
Svetoslav Borislavov

Smart UI Team
https://www.htmlelements.com/