Success!

I uninstalled, deleted my configs, and reinstalled and the first thing I did was to cut and paste from your post above into my new userchrome.css

I was very careful as my system currently opens the css file from the Joplin menu in LibreOffice Writer
Although I always save as text, I just shut LO straight after it was opened by the Joplin menu - thus generating the css file, and then edified the css in xed

Now to get back to where I was with sync and dark and a keybind I changed (indent)