Menu bar entries barley visible in dark mode

[susnux]

Describe the bug
If the browser requests a dark color theme the menu bar entries are barley visible,
except the "add image", "heading" and "formatting help" buttons all other buttons are black on dark grey (while those three work and are shown as white on dark grey).

Screenshots

Client details:

• Browser: Firefox 101
• Version: NC @ master, text @ master branch

[juliusknorr]

Seems to come from 37fef5d, will push a fix.