Css盒子模型的应用

*{    margin: 0px;    padding: 0px;}.top{    width: 100%;    height: 50px;    background-color: black;}.top_content{    width: 75%;    height: 50px;    margin: 0px auto;    background-color: blue;}.body{    margin: 20px auto;    width: 75%;    height: 1500px;    background-color: blanchedalmond;}.body_img{    width:100%;    height: 400px;    background-color: darkorange;}.body_content{    width: 100%;    height: 1100px;    background-color: blueviolet;}.body_no{    width: 100%;    height: 50px;    background-color: aqua;}.footing{    width: 75%;    height: 400px;    background-color: indigo;    margin: 0px auto;}.footing_content{    width: 100%;    height: 300px;    background-color: darkseagreen;}.footing_subSav{    width: 100%;    height: 100px;    background-color: black;}