Haha, I never played in "hard" mode because it was too challenging for me. That's probably why I didn't optimize the performance as much in that mode.
Thanks for the feedback!
It is.
To be hones I played it now in "hard" and the peformance was absolutley fine.
I know that some browsers has still issues when it comes to pure CSS animations as they are running on the GPU and when the Hardware acceleration is disabled the CPU goes sometimes crazy.
I had the same on an animation GitHub a while ago used on their landing page.