.square, .circle {
    width: 100px;
    height: 100px;
    display: inline-block;
    margin: 10px;
}

.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;
    padding: 20px;
}