Hi there again Lena
Since our last correspondence I temporarily changed the Wp theme on mt site to the 2019 WP theme and the customizer worked. However, it seems the CSS codes you mention are pre-built into my theme.
I approached my theme developers about the customizer issue with css and their response is:
Hi,
Here is what you can do, remove the float on the header.
Then once the plugin page appears send us a link and we will troubleshoot to fix the header. Otherwise, we have no way of knowing which code to troubleshoot for as we are not familiar with that plugin. Re-installing the theme will not help. You should get back to the developers of the plugin and ask them why their plugin does not show on some themes again.
So now it looks like I have to spend a lot of time troubleshooting with my theme provider when I would prefer to be doing more T-shirt designs.
If there is anything you can do at your end RE: the customizer not working in all themes I would very much appreciate it.
Regards
Wen