Dropdown problems

[AdRiley]

A few dropdown regressions/defects:

### Tasks
- [x] When more options than fit, the next option should be half cropped so the user can see there are more options
- [x] Scroll bar has gone, which means I can't scroll if I don't have a scrollwheel
- [x] Z-Order is wrong, should appear on top of the wheel menu
- [x] I think the left hand edge of the dropdown should align with the left hand edge of the widget that opens it

2023.2:

2023.3.1-rc1

[farmaazon]

May regressed in #10607 - I simplified CSS there, and probably simplified too much without taking notice.

[kazcw]

@AdRiley

Scroll bar has gone, which means I can't scroll if I don't have a scrollwheel

Overlay scrollbars are now default for Electron/Chrome on OS X. Shall we override it to get something more like the previous behavior?

[enso-bot[bot]]

Keziah Wesley reports a new STANDUP for yesterday (2024-08-19):

Progress: Started fixing dropdown issues. It should be finished by 2024-08-24.

Next Day: Next day I will be working on the #10666 task. Same task.

[enso-bot[bot]]

Keziah Wesley reports a new STANDUP for yesterday (2024-08-20):

Progress: Fixed remaining dropdown issues. It should be finished by 2024-08-24.

Next Day: Next day I will be working on the #10686 task. Fullscreen changes