body:after {
  content: '';
  position:fixed;
  background: url(https://images.chesscomfiles.com/uploads/v1/theme/1127502-0.54f01ffd.png) center center;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
  height:100vh;
  top:0;
  left:0;
  right:0;
  z-index:-1;
}

#sb .nav-panel-theme-bg {
  background-image: url(https://images.chesscomfiles.com/uploads/v1/theme/1127502-0.54f01ffd.png);
}

#sb .nav-panel-shade {
  background: rgba(0,0,0, 0.4);
}

.using-nav-horizontal:before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  z-index: -1;
 background: -moz-linear-gradient(to top, transparent 0, transparent 0, rgba(0, 0, 0, .25) 100%);
  background: -webkit-linear-gradient(to top, transparent 0, transparent 0, rgba(0, 0, 0, .25) 100%);
  background: linear-gradient(to top, transparent 0, transparent 0, rgba(0, 0, 0, .25) 100%);
  height: 52px;
}