I would generally caution against doing toggles with CSS. While it can be done, it often has surprising effects, and can be difficult to make properly accessible (for example in the case of opening the navigation, I don't believe it's possible to set the correct aria tags to indicate that the toggle is a button that is showing/hiding another element on screen).

Instead, for a brochure site like this, I'd rather have the links just always visible, because this is the reference site for Ruby and I imagine a lot of people find them by searching "Ruby", coving l clicking the homepage, and scanning for the link to the docs/downloads/etc.

Alternatively, if the show/hide feature is really that important, right now I would (a) explore whether it can be done accessibly using the new invoker API, so you don't need JavaScript at all (with a JS fallback), or (b) just do it in JavaScript directly, but with an accessible default if the JS doesn't get loaded properly.

But yeah, the rest I largely agree with. There's a bunch of stuff here that would have been simpler, and arguably also easier, if they'd taken a slightly different approach.