CSS is not deCSSed!
If you want to play around with Play/Pause for future animatics, you can check some of my pens, the ones that have a triangle-shaped play button in the middle. I needed my anims to be paused by default, because my animations have hundreds of objects flying around.
I also have another, yet untested theory on how to handle a CSS-only restart button. You could do it with a single checkbox - the animation being run when the input is checked, then revert to initial state after completing it. The problem is that you;d need to un-check the input and then check it again to re-run the animation. BUT you could also use two identical radio inputs. Clicking one radio input automatically unchecks the other. Only one of them would be showed at a time - the one that is not checked and needs to be clicked to re-run. Again, haven't tested it thoroughly enough to guarantee this'd work, but it's at least worth a try - if, that is, any of this makes sense to you or isn't too much of a bother.