h1,
body{ margin:0px; padding:0px; position:fixed; }
h3 {text-align: center;}
.blue-square-container {text-align: center;}
.blue-square {
  background-color: #0074D9;
  width: 100px;
  height: 100px;
  display: inline-block;
}
.yellow-square {
  background-color: #FFDC00;
  width: 100px;
  height: 100px;
  margin: 0 auto;
}
.green-square {
  background-color: #3D9970;
  width: 100px;
  height: 100px;
  position: absolute;
  left: 50%;
  margin-left: -50px;
}