That does look nice, though the price is pretty off putting. Maybe there'll be more content, maybe there won't be... I wish I was in a position to be able to support projects I wish to see come to fruition at that level, but personally I am not, especially for how little css I write.
I do hope it has or gets enough support to keep adding content though, as the level of quality is definitely a step above most free tutorials.
If I did have a complaint, it would be that i am unconvinced that using custom elements for layout is a great idea. It might work really well for apps, but isn't what I would think of as terribly semantic.
I can vouch for the paid content (and I paid the pre-pandemic price).
As for the implementation, it's possible to apply the axiomatic styles to standard HTML (directly, or via React, Vue etc). The examples happen to use web components (custom elements) bc of author preference, I think. I prefer React bc it has a better SSR story and doesn't require JS to be enabled.
As for semantic markup per se (a tangent, given my explanation above), your a11y efforts are waay better spent elsewhere.
I do hope it has or gets enough support to keep adding content though, as the level of quality is definitely a step above most free tutorials.
If I did have a complaint, it would be that i am unconvinced that using custom elements for layout is a great idea. It might work really well for apps, but isn't what I would think of as terribly semantic.