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