Board Thread:Support Requests - Getting Technical/@comment-301511-20150404011246/@comment-452-20150404013551

I've found CSS on that wiki hard to explore also.

The concept you are referring to is typically called a "throbber", but "loading icon" also works.

Found it: http://tardis.wikia.com/wiki/MediaWiki:Common.css

background-image: url(http://images3.wikia.nocookie.net/tardis/images/c/c6/TardisLoader.gif); background-size: 242px 200px; background-repeat:no-repeat; background-position:top center; background-color:transparent; overflow:visible; height:200px; width: 600px; }
 * 1) EditPageEditor .loading-indicator .loading-message .loading-throbber {