You could and that's basically what TeX does, just without the CSS. There are even typesetting systems similar to (La)TeX, that can take XML as input, see Conte

You could and that's basically what TeX does, just without the CSS. There are even typesetting systems similar to (La)TeX, that can take XML as input, see Context [1] or Sile [2]. They’re just a step away from using HTML + CSS. Why isn’t there such system? I do not know. [1]: https://wiki.contextgarden.net/XML https://wiki.contextgarden.net/XML [2]: https://sile-typesetter.org/ https://sile-typesetter.org/