Edit in JSFiddle

body[data-role="externalEmbed"] {
  background: none;
}

// Or

body.ipsApp {
  background: #666666 url(//content.invisioncic.com/Mwarframe/pages_media/forums_background.jpg) no-repeat fixed center top;
}

// Or

body:not([data-role]) {
  background: #666666 url(//content.invisioncic.com/Mwarframe/pages_media/forums_background.jpg) no-repeat fixed center top;
}