Aha! I had a look to confirm, and you are right! In essence, html + css is not. However if we have a human hitting tabs and spaces for a long enough time, then for all intents and purposes, perhaps it is? Anyhow, it's still very impressive that we can do a lot of complex computations simply by hitting tabs and spaces!
AFAIK, CSS + HTML is not Turing complete, but CSS + HTML + "Human pumping tab and space" is, which makes infinite loops less of a problem.