Discovered by @Rolograaf:
Issues:
I checked and these issues seem to apply to the base theme, with no CSS applied.
There is also the issue that if you go into any of the "full page" setting screens and return to Joplin the main toolbar labels disappear. For that @laurent suggested that, although he was aware, the impending design change meant that it was not something that he believed needed fixing at this time (my precis). I am in no way suggesting that there is anything wrong with this just suggesting that it is possible that priorities are being adjusted based on impending changes. TBH if @laurent feels that fixing UI issues at this stage, prior to a full UI update, is not a priority I can live with that 
@uxamanda BTW thanks for all your input on css and customisation I have learnt so much!! (and I am sure will forget most of it but some will stick!!)
@dpoulton that makes sense to me, I am more than happy to wait for the design change, especially since it is just a cosmetic issue. I will leave this topic up in case anyone else searches for the issue in the meantime.
As for CSS, ha! Glad to be of help. 20 years of banging my head against the wall finally put to some use :-)! I will say with Flexbox, Grids, calc, and variables, I finally am pretty happy with the stock set of tools.