User blog comment:HTF1234/It's almost time/@comment-31199204-20170129025526/@comment-4834197-20170129035352

Ah. I see.

Anyway, background can be changed via Theme Designer. Sidebar and main page require editing templates (Template:Happy_Tree_Friends_Fanon_News and Template:MainPage (and its sub-templates MainPage/Slider and MainPage/Intro), respectively) to change their visuals/content.

Reading the Source mode content might confuse you if you're not used to the format, but if you play around and hit the "preview" button (thus not publishing it) every edit you can see what changes happen caused by your edit.