Improve the display of certain UI elements in true-black mode

[chrigi]

Is your feature request related to a problem? Please describe.
When using a theme & the true-black mode some UI elements get dimmed too strongly and don't look great.

Describe the solution you'd like
Some UI elements like the bottom menu bar and the reader UI could keep a more vibrant color or get other hightlights to distinguish them better.

Describe alternatives you've considered
Making them completely black as well which might work as well.

Additional context
It looks waaay more discernable on this screenshot than it is on the actual device. The background colors of the UI elemnts are barely visible and look very strange on the device.