CSS v WAAPI.
In early 2019, we made a leap from CSS keyframe animations to the Web Animations API. If you're rethinking your approach to UI Animations for the web, this article is definitely a must-read.
You should be using the Web Animations API for your sites and web apps. It’s an extremely powerful and nearly cross-browser approach for animating DOM elements. But, don’t take our word for it. There are a lot of interesting opinions out there in favor of WAAPI.