codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="it" xml:lang="it">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>xhtml 1.0</title>
<style type="text/css">
* {
margin: 0; padding: 0;
}
body { text-align: center; }
#site {
background : #ccc url(immagine-nera-200x1.gif) top left repeat-y;
width : 800px;
height : auto;
overflow : hidden;
margin : 0 auto;
text-align : left;
}
#areasx, #areadx {
float : left;
display : inline;
}
#areasx { width : 200px; margin-right: 10px; }
#areadx { width : 590px; background : #fff; }
#header { height: 80px; border : 1px solid #0c0;}
#main { height: 300px; height: auto !important; min-height: 300px; border: 1px solid #c00; }
</style>
</head>
<body>
<div id="site">
<div id="areasx">
spalla
</div>
<div id="areadx">
<div id="header">header</div>
<div id="main">main</div>
</div>
</div>
</body>
</html>
prepara un immagine 200px x 1 di colore nero e caricala come evidenziato.