I’ve reverted back to Canvas theme and put the same code in custom.css, and it’s working ok.
Why would it work there but not in a child theme? Have I mucked up child theme creation or implementation somewhere?
If I have to update Canvas to a new version in future is there a danger of custom.css content being lost? This risk, if it is one, is why I was leaning towards a child theme as best practice.
Thanks for your help