HTML + CSS is only half of the equation. The renderer is also important. So you need a layout engine that turns the HTML+CSS into something you can view. Most

HTML + CSS is only half of the equation. The renderer is also important. So you need a layout engine that turns the HTML+CSS into something you can view. Most of the time, this is one of the browser engines, but there are many more things. There is e.g. weasyprint to produce PDFs from HTML and CSS, which would be the closest alternative to LaTeX taking HTML+CSS as input. For simple documents, it's a much cleaner alternative, I used it to autogenerate documents in a python backend.