div#lo {
  position: absolute;
  width: 500px;
  height: 360px;
  left: 0px;
  top: 0px;
  background-color: #fff;
  }
div#ro {
  position: absolute;
  width: 500px;
  height: 360px;
  left: 500px;
  top: 0px;
  background-color: #999;
  }
div#lu {
  position: absolute;
  width: 500px;
  height: 360px;
  left: 0px;
  top: 360px;
  background-color: #999;
  }
div#ru {
  position: absolute;
  width: 500px;
  height: 360px;
  left: 500px;
  top: 360px;
  background-color: #fff;
  }