Looks good, you did a good job with it. Are you planning to sell it, use it yourself, or open source it?
Good work, but doesn't "Pure CSS" usually mean "CSS without JavaScript"?
I've noticed this too. A lot of demos claim to be pure CSS but not so when view source'd.
The Javascript is only for demonstrating the functionality. It does not effect the styling in anyway, this is the job of the CSS.
It is also worth mentioning that in any application which would use a progress bar, it would require JS to calculate progress, or update the DOM to display it.