Normally LibreOffice would pick up on your theme automatically, strange why it’s like this. Are you using any different versions of LO? Flatpak version or Appimage? Appimage has a lot of issues with theming.
This one’s an easy fix though, just go to Tools > Options > View and pick a theme option, that should work. If that doesn’t help then try re-installing or using a different version.
Hope this was helpful!
Strange though, I’ve never had issues like this with flatpak… It might be possible ofc that it is flatpak but I suspect it’s the theme itself that’s faulty. Thanks for providing a solution btw!