[bawolff]

It is (and has been since the css 2.0 era) if you include user clicking mouse.

There is a famous demo of rule110 in css at http://eli.fox-epste.in/rule110-full.html

[potiuper]

Mouse is not necessary using CSS 3 (animations); Minesweeper[1] is enough to show Turing completeness.

[1] http://web.mat.bham.ac.uk/R.W.Kaye/minesw/infmsw.pdf

[James0x57]

edit: ^ previously said "with css variables to hold state" or something similar (or my wires got crossed and I saw that somewhere else)

CSS variables can't be set by animations yet without JS's CSS Houdini giving them a type - a CSS @ property is in the works to do it without JS though!