.square, .circle { 
    width: 100px; 
    height: 100px;
    }
    .circle {
    border-radius: 50%;
    }
    #blockRed {
        background-color: red;
        position: static;
        }
    #blockBlack {
        background-color: black;
        position: relative;
        }
    #container {
        background-color: blue; margin: 0 auto;
        width: 400px;
        }