MediaWiki:Common.css

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video#bgvideo { 
  position: fixed;
  top: 50%;
  left: 50%;
  min-width: 100%;
  min-height: 100%;
  width: auto;
  height: auto;
  z-index: -100;
  -ms-transform: translateX(-50%) translateY(-50%);
  -moz-transform: translateX(-50%) translateY(-50%);
  -webkit-transform: translateX(-50%) translateY(-50%);
  transform: translateX(-50%) translateY(-50%);
  opacity:.3;
}
.center1 {
    width:100%;
    height:100%;
    position:absolute;
    display:table;
}
.center2 {
    display:table-cell;
    vertical-align:middle;
    width:100%;
    height:100%:
}