This is what the #rust book (and I guess most Rust documentation, since the Rust book was generated using the same tool) looks like in #emacs' integrated browser, "eww". A bit concerning when you consider that these are static pages of mostly text-based information - why doesn't it look more accessible?
@pmidden my guess: nobody expected it to be viewed without any CSS as that's incredibly rare.
Maybe you'd prefer the Print/PDF version, which you can get by opening it in a modern browser and clicking the printer icon top-right?
@pmidden ir has a key binding to make pages more readable. r maybe?