Another small issue I've found: the "npm install reakit" textarea is focusable but doesn't have a focus ring (your code examples all do). It's not as important, as this only affects your documentation page, but I'd either add a focus ring or disable the focus altogether (as the field is not editable).
This is the best project I've ever done in my 17 years of programming. I'm sure it'll help companies ship accessible web apps with ease.
Feedbacks are welcome.
I will admit that it took me a bit to appreciate the extent of what the library supports browsing on my phone. It wasn’t immediately obvious to me I could slide the tab bar on the main page, or that the component listing was in the hamburger menu after clicking the components link. So I had to go hunting a little bit. Also it is not possible to access the last item in the components list in mobile safari, the navigation bar obscures it. I’m not sure how much you’ll want to prioritize the mobile experience of the site, but if you do I hope this feedback helps.