[PaulHoule]

Frameworks are going from the frying pan to the fire.

There are numerous React frameworks that supply a "widget set" either of web page elements, UI controls or both that work out of the box.

If you (your client, your employer, ...) like the way these look out of the box they are a great way to build something quickly and not have to understand the underlying CSS.

If you are required to customize the look, however, or you want to combine components from various sources and have them look consistent you have to understand all the concepts of the frameworks, the frameworks the frameworks depend on and CSS.