.container {
  position: absolute;
  width: 500px;
  height: 500px;
}
.box {
  width: 100px;
  height: 100px;
  position: absolute;
}
.red {
  background-color: #ff7b7b;
  top: 40px;
  left: 40px;
}
.green {
  background-color: #4effa1;
  top: 160px;
  left: 160px;
}
.blue {
  background-color: #7b7bff;
  top: 100px;
  left: 100px;
  z-index: 10; 
}
/*  */