Personally, I think class is too blunt an instrument — it breaks encapsulation, allowing component consumers to change styles that they probably shouldn't, while also denying them a predictable interface for targeting individual styles, or setting theme properties globally

We also believe that this explicit API should be relatively granular and work at the selector or value level, not at the element level. This is why we think classes are "a blunt instrument", as Rich put it. Exposing even a single class gives you a clear entry point to the entire component's markup allowing complete control over every aspect. We need a more granular way for a component to define an explicit style interface.