Board Thread:Support Requests - Designing Your Wikia/@comment-26437262-20150302123325/@comment-452-20150302163932

When you say "change the chat background for a user", do you mean
 * A: "When a user goes AFK, change the background of the chat that only they see on their computer"

or
 * B: "When a user goes AFK, change the background behind their username that everyone can see"

?

To me, it sounds like you're talking about A, but I don't understand why you would want to do that.

B, on the other hand, is easy: .Rail .User.away { background: red; }

BTW:
 * HTML = The source of a webpage. HTML can be used in articles and templates.
 * CSS = The style rules for a webpage. CSS does not alter the HTML itself, it just changes how it is displayed.
 * JS = A scripted program that runs on a webpage.  JS can alter both the CSS and the HTML itself.