It's both HTML and CSS, though. HTML is also bleeding over the boundary between layout and document.
HTML was mean to _be_ the document. CSS was meant to be a language for styling and re-styling those documents. That makes sense in the logic of decades past. You might have a bunch of documents, and go re-style them all when you move. Or a company might do this when they change their logo or get acquired.
But for a long time now almost every HTML document served on the web has long been a mix of design elements and one or more things that a human would call distinct documents, and CSS has kept up with styling those.
With a true "document", it's pretty sane to expect that you can readily style and re-style the same document with different stylesheets for different contexts without needing to go fiddle content. With full complex designs implemented in HTML, the HTML and CSS for at least those parts tend to be very tightly coupled and very likely to get rewritten together.
The fuzzy boundary between the content and the layout are a problem for both HTML and CSS.
HTML was mean to _be_ the document. CSS was meant to be a language for styling and re-styling those documents. That makes sense in the logic of decades past. You might have a bunch of documents, and go re-style them all when you move. Or a company might do this when they change their logo or get acquired.
But for a long time now almost every HTML document served on the web has long been a mix of design elements and one or more things that a human would call distinct documents, and CSS has kept up with styling those.
With a true "document", it's pretty sane to expect that you can readily style and re-style the same document with different stylesheets for different contexts without needing to go fiddle content. With full complex designs implemented in HTML, the HTML and CSS for at least those parts tend to be very tightly coupled and very likely to get rewritten together.
The fuzzy boundary between the content and the layout are a problem for both HTML and CSS.
I picked at this problem in a post this fall: https://t-ravis.com/post/doc/what_color_is_your_markup/