it's fun, i like how at first i was like "ok this game is too easy" and after the mouse wheel scrolling i was like "ohhh shit it's not easy at all"
I have maybe one or two suggestion for balancing difficulty. For me the hard difficulty was almost easier than the easy because it's moving at the same speed. In hard mode once you in the rythm you'r "ok". And hard difficulty is more forgiving about going too far in the progress bar. Since the bar is going down quicker.
So if you want to make the difficulty going really hard i think you can add some randomness at the speed of every progess bar. Like the speed is changing over time. So the player have to check how every progress bar is moving all the time ( and maybe if you do that, slow down the speed a little bit or it will be impossible for human ).
And at the easy difficulty maybe you can make the progress bar go down faster when you over shoot one of the input. Cause i died many time smashing too much one of the input and i died before it was going down in the safe spot.