#example{
    position:relative;
    width:500px;
    height: 500px;
    background-color:#263238;
    z-index:10;
}
.square{
  position: absolute;
  width: 50px;
  height: 50px;
  z-index: 20000;
  background-color: #3498DB;
}
#s1{
  left: 150px;
  top: 200px;
}
#s2{
  left: 350px;
  top: 200px;
}