[Uristqwerty]

With transition:, width:, and :hover, I was able to make an element repeatedly cycle between states with the only user input being to leave a cursor positioned over the page.

Maybe it's a browser-specific quirk; maybe it uses features only implemented after the initial explorations of turing-complete CSS; maybe there isn't any way to hook the two together. CSS will continue to add features over the years, though, and each added feature is another chance to find a missing piece that makes turing-complete CSS easier, more possible, and/or more powerful.