> Custom properties can be applied to any element as well. Well, no, they can't. That's the point the article is making. Classes can compose arbitrarily, i.e.

> Custom properties can be applied to any element as well. Well, no, they can't. That's the point the article is making. Classes can compose arbitrarily, i.e. class="size-small size-big" Whereas data-size="small big", while valid syntax, would not be styled by a rule targeting elem[data-size="small"]