A specific site demonstrating how CSS works?

Question

Design

For a long time I saw a demo page on the Internet, the appearance of which could be changed on the fly, poking at buttons like. The content remained unchanged, only the design changed. The essence of the idea was that only the CSS file applied to the page changed, a sort of visual aid of CSS work. Also, anyone can create their own CSS file for this page and upload it to this site. After approval, it was added to the list of these very CSS. Maybe someone knows him, or something like that. I want a link))

Answer 1

www.csszengarden.com/200

Answer 2

jquery.com