Design/Living style guide

A living style guide offers improved documentation of the visual appearance and behavior of a site. Unlike a static style guide (say, a wiki page or PDF), it is generated on-the-fly from the actual HTML, CSS, and JavaScript used in production. This allows us to view styles as they are live on the site, and inline comments can be added to document the purpose of a particular style or set of styles.

MediaWiki's style guide can be found at https://design.wikimedia.org/style-guide/

Its source code is located in wikimedia/WikimediaUI-StyleGuide at GitHub.

When you use OOUI components within MediaWiki, they use its WikimediaUI theme which has its roots in mediawiki.UI.

OOUI library live demos
This OOUI library features a live demo environment with all JS & PHP components and their JavaScript code snippets.