Application theme not applying completely

### Microsoft PowerToys version

0.100.0

### Installation method

PowerToys auto-update

### Area(s) with issue?

General

### Steps to reproduce

I've also had this issue before the update, think I was on 0.97.x then. When I change the theme to dark theme, the theme only changes for the powertoys main window, but not for small popups like the quick access flyout or the FancyZones editor. They all stay in light theme, no matter whether I set to dark or follow system theme.

### ✔️ Expected Behavior

The theme set in General section applies to every window or popup from PowerToys.

### ❌ Actual Behavior

The theme set in General section only applies to the main window.

### Upload Bug Report ZIP-file

_No response_

### Additional Information

Windows 11, ran as admin, system Language English UK.

### Other Software

_No response_

Reproduce the issue in PowerToys 0.100.0 on Windows 11 by changing the General theme to dark or system-following. Compare the main window with the quick access flyout and FancyZones editor; done means the selected theme applies consistently to every listed window and popup.

Written by the indexing model from the issue text.