/*common css*/
*{padding:0;margin:0}
.clear{clear:both}
body{font-family:arial;font-size:13px}
#wrapper{width:100%;height:600px}
#header{width:100%;height:50px;background:purple}
#content{width:100%;height:600px;background:orange}
#left{width:30%;height:600px;background:pink;float:left}
#right{width:70%;height:600px;background:green;float:right}
#footer{width:100%;height:50px;background:purple}

#chagebg{background:yellow;width:300px;height:100px;}