And to spell it out:

- Stylesheet encoded as base64 in the Link header;

- Browsers always implicitly have at least the html and body tags;

- CSS cannot create new elements, but it does get 2 free pseudo-elements per actual element, ::before and ::after;

- CSS can set textual content for pseudo-elements;

So, it sets content to a pseudo element of an implicitly created tag, that's why the page is so minimal.

(Well, it could be up to 4 times as complicated I think, by using the other 3 pseudo-elements. Or cheat by using a big SVG as a background-image with more complex contents, but then you start running into header size limits and whatnot)

ah, thanks!

Seems like 'stylesheet' is only supported in Firefox: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Li...

It works with Firefox. It is pretty clever - (mis)uses the HTTP link header, which doesn't seem to be supported with Chrome.

Does there need to be one? It raises awareness of the headers used, even if they’re used weirdly here.

It does not really work on all browsers, but I can imagine scenarios where in some network middleware you have some dynamic control over headers but don't have control over the content, so that might be once place something like this could be useful.

One could leverage this as a clever way to update something on a page without redownloading it. Or from a proxy, without having to decompress & process body. Unfortunately support is limited to Firefox, so it's useless.