Imports custom JavaScript and CSS into all Discussions on Fandom via a Chrome/Firefox Extension. Documentation is available here.
Aside from custom JavaScript and CSS that users supply for importing, this extension also imports jQuery version 3.3.1, whose minified code can be found here, non-minified code can be found here and the source code can be found in the jquery/jquery 3.x-stable branch on GitHub.
You will be provided with credentials to the CustomizeDiscussions account on Fandom. Upon loading the extension without further configuration, its global Discussions JavaScript page should load on any instance of Fandom Discussions, for example, on Fandom Developers Wiki.