Wow, things have come a long way.

When CSS3 and jQuery first started gaining some traction (<8 years ago?), I tried a bunch of animations using layered images and image transformations. One of these "dreams" was of some hot air balloons as well. Desktop only:

https://technotarek.com/sky (first balloon appears at ~10s)

My favorite was a simple tail wag (https://technotarek.com/cat).

Edit: noted desktop only