This seems needlessly nitpicky. You need JavaScript to view the embedded CodeSandbox, which is an interactive application within an iFrame. Good luck making what's effectively an IDE without JavaScript.

I suppose the author could show the CSS snippets inline and make you click to a demo, but that's not very fun is it?

You don't need an entire IDE to show examples of content styled with CSS.

The anti-JS mindset (I assume for privacy reasons) seems so backwards to me on a social bookmarking site targeted at programmers/technologists.

We wouldn't have this mindset if sites retained enough basic functionality with it off, which is totally possible. I use NoScript pretty aggressively, and it's astounding how many sites actually render nothing unless you have JS turned on. Browsers and backends both implement form validation, yet most sites today don't support submitting a basic form without JS. I'm not expecting things like Spotify and YouTube to work without JS, but I should be able to at least read most webpages without running full-fledged applications with 7 different tracking scripts and 5 custom fonts.