.square{
    width: 100px;
    height: 100px;
    display: block;
    
}
.circle{
    width: 100px;
    height: 100px;
    display: block;
    border-radius: 50%;
    
}

#blockRed{

    background-color: red;
    position: relative;
}
#blockYellow{

    background-color: yellow;
    position: relative;
}
#container{
    background-color: blue;margin: 0 auto;
    width: 400px;
    background-image: url("beijing.png");
}