Allow to change a Theme without requiring a restart

[epomatti]

• [X] I agree to follow the Code of Conduct that this project adheres to.
• [X] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Is your feature request related to a problem? Please describe. No.

Describe the solution you'd like

When I select to change a theme, it is only applied after a restart. It would be nice to have the theme applied immediately. In my case, I work with several projects and they use different styles.

Describe alternatives you've considered n/a

Additional context n/a