Well they could have a list of the properties without them all rendered and then render just the property they need when someone clicks on the property name.

And why should it render all examples on one page?

They could have a static page for every property so one could link to http://cssreference.io/align-content instead of http://cssreference.io/#align-content and get just that static page. That should be pretty quick, especially with long caching of all other resources than the actual page content.

There's lots of different ways to have done it without having to do it all at once.