I remember a few years ago I found some sort of free model that actually did a pretty good job at parsing HTML into guis. I don’t think JS or css (or images/site assets for obvious reasons) were supported, but technically there shouldn’t be anything stopping you from reading basic data.
I would think you could go through the long and tedious process of parsing out each HTML tag and translating it to a GUI in game. I’m assuming it will be long and tedious. CSS will only add to this complexity but is still doable. As for JS, that’s a bit iffy. JS is an actual language so you’d essentially have to create your own compiler or something.