I’ve been reading my way through the WHATWG Living Standards for HTML. And that led me to a specification listing the features of HTML and CSS that can be used to format material for print production.
The author of this standard is Håkon W Lie who first proposed a Cascading Style Sheet scheme for HTML documents in 1994 while working at CERN.
He states that HTML and CSS are already used by publishers to produce printed media with one company offering very expensive commercial software.
If anyone is interested in knowing more, here’s a link to an introductory guide.