LO 5.1.42 on Ubuntu 16.04.
In LO Writer, the font in the tabs on dialog boxes - for example, the tabs for the “Bullets and Numbering” dialog box - are white, against the light gray background of the dialog box, making the titles of the tabs unreadable.
How do I fix that?
Did you try to remove libreoffice-gtk i libreoffice-gtk3 packages? (these are the commands for the terminal “sudo apt remove libreoffice-gtk” and/or “sudo apt remove libreoffice-gtk3”. You can remove them without fearing your LibreOffice will be affected. And you can install them back if you find it did not help you.
Ljiljan got me on the right track. I had to uninstall libreoffice-gtk3 only in order to solve the problem. Thanks.