..square, .circle {
    width: 100px; 
    height: 100px;
}

.circle {
    border-radius: 50%;
}

#blockred {
    background-color: red;
}
#blockyellow {
    background-color: yellow;
}

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

#blockWood {
    background-image: url(wood.jpeg);
}

<div class='square' id='blockred' style='top: 200px;'></div>