#container {
    background-color: lightgray;
    width: 400px;
    height: 400px;
    margin: 0 auto;
    position: relative;
}
.square, .circle {
    width: 100px;
    height: 100px;
    position: relative;
 }

 .circle {
    border-radius: 50%;
 }

 #redSquare {
    background-color: red;
    top: 20px;
    left: 20px;
 }

 #yellowSquare {
    background-color: yellow;
    top: 40px;
    left: 120px;
 }

 #blueCircle {
    background-color: blue;
    top: auto;
    left: 80px;
 }

#greenCircle {
    background-color: green;
    top: 80px;
    left: 180px;
}