Very same theme I used for my demo as it doesn't work for the newest theme UNA has provided for UNA 13.

I find it hard to believe there could be a conflict with third party modules that differ from my own install as it's a very trivial CSS addition.

You’re using it on Una 13? I’m still on 12.

Yes I'm running 13, it's a non-production site, using it to test a few things.