Setting a default GUI theme still breaks the editor

[badunius]

Godot version

v3.4.4.stable.official [419e713]

System information

Windows 10, GLES3, GeForce GTX 1650

Issue description

This issue was fixed according to this message, but apparently it still persists.

This time however GUI elements appear to be scissored

Color picker

Autocomplete (it's there, I can use keyboard to complete, but the list is effectively invisible)

Steps to reproduce

1. New resource... > Theme
2. Open it in Theme editor
3. Manage Items... > Import Items > Select All > Import Selected
4. Save the theme
5. Project Settings > Gui > Theme > Custom Theme
6. Select the theme, press Save & Restart

Minimal reproduction project

https://github.com/badunius/godot-theme-bug-repro

[KoBeWi]

Seems also happening in 4.0. It's not as severe, but some nodes are affected for some reason:

[YuriSizov]

The 4.0 issue was addressed by #75566, but this is still relevant, with more problems in 3.x. So in case someone wants to fix these for 3.x, I'm keeping the issue open in the correct milestone.

[ninstar]

If you try to make a theme that uses all properties available, some of them will still break the IDE in 4.x, all of them seem to be only affecting margin and separation values inside and outside styleboxes.