#container {
 background-color: blue;
 margin: 0 auto;
 padding: 0;    
 width: 400px;
 height: 400px;
}
.square, .circle {
 width: 100px;
 height: 100px;
 display:inline-block;
 float: left;
}
.circle {
 border-radius: 50%;
}
#blockRed {
 background-color: red;
}
#blockYellow {
 background-color: yellow;
}
#blockWood {
 background-image: url(wood.jpg);
}
#blockWhite{
    background-color: white;
}