Board Thread:Support Requests - Designing Your Wiki/@comment-120.56.111.22-20180208084620/@comment-9605025-20180208095826

It depends on what you have in mind, but you must register an account. If you want to apply the JS (JavaScript, not Java; there is a big difference) to a wiki such that all users see it, then you must be an admin on that wiki. If you want to apply it just for yourself, then you can use your personal JS (again, you need to register an account first). If you want to apply it to all wikis you visit, import the JS in your global personal JS. If you want to apply it to one particular wiki, import it in your wiki-specific personal JS. To do that, go to the wiki on which you wish to have the animated background and then go to "Special:MyPage/common.js" if you want to apply it for all skins or the skin-specific JS (likely "Special:MyPage/wikia.js") if you want it applied to only one skin.