Build Config: Configure Theme

[maxammann]

Is your feature request related to a problem? Please describe.
In the build config from #517 we already defined that a theme must be configured.

This issue requires #513 to be done.

Describe the solution you'd like
Maybe adjust the definition of a theme and use this for theming the app.
Mostly colors should be adjusted in this PR. No new components should be created.

Describe alternatives you've considered
None

Additional context
None

[maxammann]

Only existing components should be adjusted in this task. No new ones should be created.