I got it working with the CSS you posted. Thank you so much for your help.
The problem was that I originally pasted your CSS below some custom .site-info (footer code) in the child CSS.
When I moved it above that code it worked. It didn’t like being below the footer and I should have spotted that the first time. Now I know that custom footer code has to be the last thing in the child CSS which makes sense.
Thanks for this great theme and your excellent support. I’d recommend it to anyone.