div {
    width: 150px;
    height: 150px;
}
.red {
    background-color: red;
    position: absolute;
    top: 0;
    left: 0;
}
.green {
    background-color: green;
    position: absolute;
    top: 0;
    right: 0;
}
.yellow {
    background-color: yellow;
    position: absolute;
    bottom: 0;
    right: 0;
}
.blue {
    background-color: blue;
    position: absolute;
    bottom: 0;
    left: 0;
}