MediaWiki:Vector.css

/* CSS placed here will affect users of the Vector skin */

body {
  background: url(/bg.jpg) no-repeat center center fixed !important;
  -webkit-background-size: cover !important;
  -moz-background-size: cover !important;
  -o-background-size: cover !important;
  background-size: cover !important;

/*
    background-image: image-set(
       url("/w/images/1/19/BG3-Background.jpg") 1x,
       url("/w/images/1/19/BG3-Background.jpg") 1.5x,
       url("/w/images/1/19/BG3-Background.jpg") 2x
    ) !important;
    background-repeat: no-repeat !important;
    background-size: auto !important;
*/
}