.square, .circle {width: 100px;height: 100px;display: block;float: left;}

.circle {border-radius: 50%;}

#blockRed {background-color: red;}

#blockBlue {background-color: blue;}

#blockYellow {background-color: yellow;}

#blockPink {background-color: pink;}

#blockLightBlue {background-color: lightblue;}

#blockDarkRed {background-color: darkred;}

#blockDarkBlue {background-color: darkblue;}

#blockWood {background-image: url('https://images.pexels.com/photos/172276/pexels-photo-172276.jpeg');}

#container1 {background-color: yellow;
    margin: 0px auto;
    padding: 0px;
    width: 400px;
    height: 400px;
    position: relative;}

#container2 {
    background-color: pink;
    margin: 0px auto;
    padding: 0px;
    width: 400px;
    height: 400px;
  }