#blueBox {
  background-color: blue;
  width: 100px;
  height: 100px;
  position: absolute;
  left: 0px;
  top: 0px;
  margin: 0px;
}

#blackBox {
  background-color: black;
  width: 100px;
  height: 100px;
  position: absolute;
  left: 50px;
  top: 50px;
  margin: 0px;
}