Page chooser button should remain highlighted while the dropdown is open

[mstange]

Example profile

Steps to reproduce:

1. Click on "Full Range (3.4s)"
2. While the dropdown is open, move your mouse away from the button that opened it.

Expected results:
As long as the dropdown is open, the button's hover effect should remain visible.

Actual results:
The button's hover effect is lost.

Actually maybe we should have an even darker highlight, as part of a "pressed"/"open" state for the button.

┆Issue is synchronized with this Jira Task

[canova]

Yeah, this is the case for tracks list popup too. I wanted to fix it too for a while, but last time I checked it wasn't very straightforward due to the library we use, but it should be doable still.

[julienw]

and don't forget about aria attributes and states too :-)