body, header, #content, { margin:0; padding:0; border:0; 
}
/*add display attributes for the semantic tags*/
header, footer, section, article, nav { display:block; 
}
/*change #header to header and remove div*/
body { margin:auto; background:url(images/green-grad.jpg) repeat-x; 
}
header {width:920px; height:180px; padding:0; border:10px white solid; 
  background: url(images/header3.jpg); margin:10px auto; 
}