User:Spongebobguy 2/global.css

body.skin-oasis.page-User_Spongebobguy_2 { background-image: url("template.net/editable/96315/spongebob-flower-background"); }

If you want to use it for all the tabs and their subpages, use this:

body.skin-oasis[class*="page-User_Spongebobguy_2"] body.skin-oasis.page-Message_Wall_Spongebobguy_2 body.skin-oasis[class*="page-User_blog_Spongebobguy_2"] body.skin-oasis.page-Special_Contributions_Spongebobguy_2 { background-image: url("template.net/editable/96315/spongebob-flower-background"); }