[Bug] Window controls have no background when hovered over on Linux

[PavelDobCZ23]

Description
There is no background colour (or any other visual) change when hovering with cursor over window control buttons on Linux version of VSCode with any Bearded theme applied. Other colour themes do not have this problem.
Visual example of the correct behaviour using default VSCode's Dark theme:

Steps to reproduce

1. Open VSCode on a Linux system.
2. Make sure to have these 2 settings applied:
   • JSON:
     { "window.titleBarStyle": "custom", "window.experimentalControlOverlay": true }
   • In Settings Page:
     
3. Hover with your cursor over the window controls in the top right corner.
4. Observe no visual change of the background colour of the buttons.