.clear{clear:both;}
#wrapper{width:1000px;height:600px;background:yellow;}
#header{width:100%;height:100px;background:black;}
#after_header{width:100%;height:100px;background:green;}
#banner{width:100%;height:200px;background:red;}
#after_banner{width:100%;height:100px;background:black;}
#footer{width:100%;height:100px;background:blue;}
#first{width:33%;height:100px;background:red;float:left;}
#second{width:34%;height:100px;background:green;float:left;}
#third{width:33%;height:100px;background:blue;float:left;}