#container {

    background-color: blue;
    margin: 0 auto;
    width: 400px;
}

.square, .circle {
    width: 100px;
    height: 100px;
    display:block;
    position: relative;
   /* float: right; */
    }

    .circle {
    border-radius: 50%;
    }
    .blockRed {
    background-color: red;
    }
    .blockyellow {
        /*margin-top:400px,*/
    background-color: yellow;
    }