@unruhe Without any details (exact LibreOffice version, Linux distribution, desktop environment and toolkit in use) it's very hard for us to say. You can let our Design community know with a bug report at https://bugs.documentfoundation.org but please do provide lots of details about your setup, otherwise we can only make random guesses...
I tried the dark theme and setted the text color white and the background as black but your @libreoffice is full of bug. Not all text appears white, some of it still black. I used last version of LibreOffice Writer on Linux and I moved back to the light theme because of all the bugs. Did you about this?