Enable Hidden Secret Dark Theme Mode
1. In Registry Editor, go to following key:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize
2. In right-side pane, create a new DWORD AppsUseLightTheme and leave its value to 0
3. That's it. Now you can enjoy dark UI in all modern apps including Settings app.
To restore default UI, delete the new DWORD AppsUseLightTheme.
