.square, .circle {
width: 100px;
height: 100px;
display: inline-block;
float: middle;
}
.circle {
border-radius: 50%;
}
#blockRed {
background-color: red;
position: relative;
}
#blockYellow {
background-color: yellow;
position: relative;
}
#container {
    background-color: blue;
    margin: 0 auto;
    width: 400px;
    height: 400px;