#container{ 
  background-color: pink;
  margin: 0 auto;    
  padding: 0px;
  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("picture.jpg");
}