I was just a bit confused when I found out that pressing any key casts a new confetti, but pressing arrow keys doesn't do anything different from any other key.
I'd intuitively expect arrow keys to move the confettis in any direction. Or at least left/right, which would be even more expectable from fireworks since they're launched from bottom to top. By the way, moving fireworks horizontally "mid-air" just sounds dynamic and cool.
I have not tried to implement this myself (yet?), but since fireworks are launched from a random point that is (!) available on the screen, and the confettis are centered relative to the screen, I take it as not too hard of a task.
P.S. The confettis remind me of cmatrix