I haven't even read it yet but this website is exactly what I'd expect to see all sites like, customisable to your taste (and even needs, for visually impaired). And this is the first web page I've ever seen that does that since... the web began I guess.
For better or worse, some US regulations have made it a requirement for certain websites to have accessibility functionality. That has spawned a small ecosystem of plugins that aim to fulfill the regulatory requirements. Does they make for a more accessible websites? Judging by the plugins I have seen so far, I really doubt it. But it is at least a springboard to work from, and a kick in the butt for people who truly do care and are talented enough to pull it off properly.
That said, these plugins, and their failings, are a reminder to me that accessibility can't be an after thought, it needs to be baked into your product's UX.
Fictionpress and Fanfiction.net are also similarly customisable. You can change para width, font-size, background/foreground colour, and the font too (about 10 different kinds).
Font-size is trivially done by the user zooming, but the other settings probably ought to be implemented by more sites, especially text heavy ones.
