Sure, you are right about infinite non-interactive CSS animations. And it's true there are simple checkbox:checked or whatever:active hacks for interactivity without JS. But for "click to (re)restart animation" there is no better cross-browser way I am aware of than toggling on some trigger attribute and toggling it off on animation end event, hence the JS.
Ok, so here is variation that contains zero JS and (ab)uses the "invisible_anchor:focus + sibling_anchor_pointing_to_previous_anchor" trick [0]. I'd prefer the original version, though. This is more or less a hack.
