/**     common css    **/
*{margin:0;padding:0;outline:0;}
body{background:blue;color:pink;font-size:20px;}
#box{width:800px;height:800px;background:#999;}
header{width:100%;height:100px;background:orange;}
#content{width:100%;height:600px;background:green;}
/**     content    **/
#layout #content-left{width:50%;height:600px;background:#408080;float:left;}
#layout #content-right{width:50%;height:600px;background:#99FF00;float:left;}


footer{width:100%;height:100px;background:yellow;}
#changebackground{background:red;width:200px;height:200px;float:left;}