I decided to give KDE a spin and turns out the theming options are extremely limited. There are only two window decorators and they are both ugly. If I want to install CDE/Motif theme, how should I do it?
This should work for many themes - Download the theme you
want, transfer it to dom0, extract it and move the folder to
/usr/share/plasma/desktoptheme
CDE comes with an installer - I haven’t tried it and cant vouch for it -
it also comes with some caveats and helper applications that you will
need to satisfy yourself.
Usual caveats about using code of unknown provenance in dom0.