I doubt very much you'll be able to directly take a website with math and get it to render correctly in the viewer. It depends very much on how mathjax is called, what css is used what output jax is used, etc. And looking at the html extract you posted its looks like the postprocessed output from mathjax, not the original markup, which is even less likely to work.
Your best bet is using either mathml for embedded latex/asciimath ina simple html page, like the example here:
https://manual.calibre-ebook.com/typesetting_math.html