That does seem sensible. I'll agree to a weaker, more specific claim like: HTML5 + CSS can simulate a Turing machine in Rule 110, but browsers aren't set up to

That does seem sensible. I'll agree to a weaker, more specific claim like: HTML5 + CSS can simulate a Turing machine in Rule 110, but browsers aren't set up to do that without user input. Turing completeness level: eh.