#overlay {
  display:    none;
  position:   fixed;
  z-index:    1000;
  top:        0;
  left:       0;
  height:     100%;
  width:      100%;
  background: rgba( 255, 255, 255, .8 )
              url('https://i.stack.imgur.com/FhHRx.gif')
              50% 50%
              no-repeat;
}