MediaWiki:Common.css

/* CSS placed here will be applied to all skins */
body { background-color: #000000; }
.wikitable { background-color: #000000; }
content { color: #FFFFFF; }

body {
    background-color: #000000;
    /* this assumes that your wiki is installed at '/w' in the web root */
    background-image: url('https://uoendurance.com/wiki/images/4/4b/EnduranceHomePageBanner.png');
    background-repeat: no-repeat;
}

#mw-page-base {
  background-image: none;
  background-color: transparent;
}