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.
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!