fix:3197: Set header to black in darkmode.
Description
In dark mode, Murena notification setting screen shows header in grey, but (most) entries in settings use same colour as the background (black). We want to align all entries to "black".
Screenshots
Now:
Issues
https://gitlab.e.foundation/e/os/backlog/-/issues/3197
10 commandments of code review
Edited by Guillaume Jacquart