I also pointed out Ariato recently: https://github.com/bigskysoftware/missing/discussions/3#discussioncomment-2192522 — it seems to not only rely mostly on semantic HTML elements, but unlike most classless and class-light stylesheets out there, it also makes use of ARIA roles to enhance styling. Not sure if @User has seen it, but it seems like it would be useful even if just for inspiration and cross-validation.