<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="it" lang="it">

<head>
<style type="text/css">
#container {
border: 1px solid gray;
margin: 10px;
margin-left: auto;
margin-right: auto;
padding: 10px;
text-align: center;
}

#banner {
padding: 0;
margin-bottom: 0;
background-color: rgb(213, 219, 225);
}

#content {
padding: 0;
background-color: gray;
width:750px;
margin: 0 auto;
}

#sidebar-a {
float: left;
margin : auto;
padding: 0;
background-color: #fc3;
}

#sidebar-b {
float: right;
margin : auto;
padding: 0;
background-color: #333;
}

#footer {
clear: both;
padding: 0;
margin-top: 0;
background-color: #ccc;
}
</style>
</head>
<body>
<div id="container">
<div id="banner"> </div>

<div id="sidebar-a">

prova</p></div>

<div id="sidebar-b">

prova</p> </div>

<div id="content"> sdfsdfsdf</div>

<div id="footer">

prova</p> </div>
</div>
</body>
</html>