We can't compose custom CSS animations but we do have bounce to work with.
Animations can be stacked in block elements with arbitrary transforms like rotations and skews applied, so by layering bounce running at different periods under different transforms you could hypothetically produce complex motion.
Tried it, but my CSS isn't great so it didn't work out. The limitation of the animation moving 25% of the element's height was a pretty big roadblock.
Still...
