[timmaxw]

I'd say that a CPU that needs a clock but does not have one is not Turing-complete. CSS plus an infinite stream of user input is Turing-complete, but CSS itself is not Turing-complete. I should make it clear that I'm not saying, "my definition is the one true definition of Turing-completeness"; just that I prefer this definition. One reason I prefer this definition is that the claim "CSS is Turing-complete" makes it sound like browsers could take unbounded time to render a webpage that only used HTML and CSS, which as far as I can tell is not true.

[Cushman]

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.