Dark mode/theme does not apply to drawing area background

[mardab]

Describe the bug or feature A clear and concise description.

• Version 44-alpha4 [flatpak]

Upon changing global theme for GTK apps, only top and bottom bars have the colors applied, while drawing area remains white.

Step to reproduce an issue (omit for feature request) Steps to reproduce the behaviour:

1. set dark theme in GTK applications theme settings or start application with valid theme variable (e.g. GTK_THEME=Adwaita:dark)
2. open Design

Expected behaviour Drawing space background colors should match selected GTK theme.

Supporting documents