Sorry I'm blind! I completely missed the live demo. I think because it's on the top right corner I instinctively ignored it.

Maybe could have a "Try live" button that sort of nudges you to it (could open the sidebar with the page structure or something to make it obvious you're in "edit mode") if other people struggle to find it

Re. diff view, yes, I think it's the kind of thing that would give reassurance to users that they can play around with it without breaking anything, otherwise I feel I'd be a bit scared of accidentally touching something that shouldn't be changed (especially as you might experiment a bit before you land on the right style to change)