I would like to report an issue with Librem Mail on android (not sure if this is the right place for this, let me know if not).
When using dark theme, if you click on the " ⋮ " menu (bottom right), it will pop up a short menu ( select all […] parameters), this menu will appear with black font over dark grey background.
This is barely readable in case the screen brightness is set low (at night for example).
In K-9, similar menu in dark mode use white font over dark grey background which is perfectly readable, whatever conditions.
Added a photo to show the issue with brightness set to minimum.