[rtsao]

You're absolutely right that you can do it with pure CSS. But doing a pure CSS solution usually involves some CSS methodology that you need to apply extremely strictly and consistently, which honestly can be a challenge, especially in large apps. Sometimes it's easier to just throw in a new selector at the end of your stylesheet and "make it work". Without discipline, things can get messy pretty quick.

The point of CSS-in-JS and CSS modules isn't that it's necessary, just that it makes avoiding these sorts of problems much easier.