Super simple note for future reference and for anyone else running into this issue. I upgraded my version of LibreOffice in Kubuntu 20.10 to a pre-release version to fix a bug. I was running version 188.8.131.52.
When I purged the version of LibreOffice that shipped with Kubuntu 20.10 (6.X – I don’t remember exactly which version), that also purged the KDE integration package that helps LibreOffice interface with the window manager and makes skinning LibreOffice much easier. As a result, when I would change my Global theme in System Settings, only part of the LibreOffice windows would change to reflect that theme. In particular, the sidebar on the right side of LibreOffice wasn’t changing colors with the rest of the window. This was making it impossible for me to see the names of different styles and also looked really weird.
The solution was easy. In Synaptic, search for the “libreoffice-kde” integration package and install it. Now, when I change my Global Theme, the LibreOffice windows change to reflect that.
In short, if you purge the version of LibreOffice in the repositories in KDE and install a newer version, make sure you also install the libreoffice-kde integration package or your LibreOffice windows will behave strangely.