div{
    height: 100px;
    width: 100px;
    position: absolute;
}
.red{
    background-color: red;
    top: 50px;
    left: 50px;
}
.green{
    background-color: green;
    top: 100px;
    left: 100px;
}
.blue{
    background-color: blue;
    top: 150px;
    left: 150px;
    z-index: 10;
}