They seem to fall at speed, but then de accelerate before touching the ground, then they bounce again until coming to a standstill.
The ball on the title looks accurate when bouncing, so I'm not sure if this is on purpose or not.
Running firefox under MacOS.
The stylesheet defines a single set of animation keyframes going from top to bottom at constant speed with a small bounce, and then applies the default CSS "ease" timing function to the entire animation. That results in an incorrect non-zero vertical initial velocity (making it seem like the ball was thrown downward rather than dropped), an initial downward acceleration that's vaguely in the right ballpark, and then a deceleration that's completely incorrect.
Firefox on Ubuntu: https://www.youtube.com/watch?v=5CihIHXj5HE
I'm guessing that this behaves differently on Chromium, or alternatively that OP has never seen a ball bounce before :)