[Bug] Theme reverts to the default one after some time

[Patrxgt]

Before Reporting

• [X] I found no existing issues matching my bug
• [X] My issue is not caused by a theme

Describe the Bug

After using Steam for an hour or so theming starts to slowly return to default one. First the small window that shows up when starting a game, then parts of the overlay when the game is running, then the store page and at the end the whole library and the top bar. It happens in the online mode, but is more frequent in the offline mode or when PC doesn't have any connection to the internet.

Expected Behavior

Theme should not change overtime.

Steps To Reproduce

1. Turn on Steam and apply any theme.
2. Restart Steam (preferably in the offline mode or turn off any connection to the internet in the network card settings).
3. Wait for an hour or two.
4. Try turning on the game.

Operating System

Windows

Anything else?

It's not really connected in any way to this issue, but the small notification that shows up when starting a game with the Steam Overlay turned on isn't themed properly and shows up as an empty rectangle in the main color of the applied theme.