[brundolf]

Edit: I partly misspoke. I assumed CSS transitions would be nontrivially more performant since it's a more declarative API and the math would be done natively by the browser, but according to MDN the performance difference is negligible in most (though not all) cases if you're using requestAnimationFrame in the JavaScript version: https://developer.mozilla.org/en-US/docs/Web/Performance/CSS...

The main case where CSS transitions are meaningfully faster appears to actually be transforms themselves, because for those the actual transition, too, can be moved to the GPU, whereas a JavaScript-driven transition still has to be run on the main CPU thread.