CSS variable libraries like open-props also do this, only without the controversial use of utility classes. Add editor snippets to that and you have nearly the same ease of use as tailwind.

Class definitions are not CSS. They're markup. The CSS selector language does let you target them (with a leading dot, as in .foo)—just like CSS lets you target other things defined in markup with special syntax: element IDs (#bar), attributes ([foo=bar]), etc. It's not as if HTML existed without classes and without CSS, and then CSS was invented and with it came classes, too.

(This isn't to say that you're alone. A frighteningly high number of people reveal through their choice of language an apparent belief that `class` was invented by the CSS working group (or something). That when you're writing HTML, evidently 95% of it is HTML proper, but then when you get to the part where you type out 'c', 'l', 'a', 's', 's', that you're shifting into CSS and it's like, "This last piece with these "classes" was contributed by the CSS folks, and so that's why/how CSS leaked in," without ever seeming to realize that... they're not actually writing CSS. It's still just markup—using the ordinary syntax for specifying attributes and their values. The CSS only happens when you, uh, start writing CSS...)