#box{width:600px;border:2px solid black;}
header{width:100%;height:100px;background:orange;}
#content{width:100%;height:400px;}
footer{width:100%;height:100px;background:pink;}
#clear{clear:both;}
/** layout 1 **/
#layout1 #left{width:50%;height:400px;background:grey;float:left;}
#layout1 #right{width:50%;height:400px;background:green;float:left;}

/** layout 2 **/


/** layout 3 **/