Ciao,

innanzitutto grazie mille per la risposta.

Posto il codice css e codice della pagina dove richiamo il css.

----------------CSS--------------------------

body
{
behavior: url(csshover.htc);
background: white;
margin: 0 0 0 0;

}


#contenitore
{
width: 100%;
height: 100%;
}


#contenitore_nuovo
{
margin-left: auto;
margin-right: auto;
position: relative;
width: 1000px;
}


#parte_centrale
{
position: relative;
float: left;
width: 100%;
background: green;
height: auto;
margin-left: auto;
margin-right: auto;
}




#banner
{
position: relative;
width: auto;
height: 120px;
background: #f1c200;
}


#logo
{
position: relative;
width: 435px;
height: 110px;
background: url('../images/logo_el_tipico_italiano.jpg');
z-index: 1;
float: left;
}


#cont_prod
{
position: relative;
width: 700px;
height: 750px;
z-index: 1;
float: left;
}


#sin_prod
{


margin-left: auto;
margin-right: auto;
position: relative;
width: 100px;
height: 400px;
float: left;
}


#des_prod
{
margin-left: auto;
margin-right: auto;
position: relative;
width: 200px;
height: auto;
float: left;
}
#rig_prod
{
position: relative;
width: auto;
z-index: 1;
float: left;
}


#prodotto
{
position: relative;
width: 150px;
z-index: 1;
float: left;
margin-right: 5px;
}


#tabella
{
border-left-color: red;
border-left-style: solid;
border-left-width: 1px;

border-right-color: red;
border-right-style: solid;
border-right-width: 1px;

border-top-color: red;
border-top-style: solid;
border-top-width: 1px;

border-bottom-color: red;
border-bottom-style: solid;
border-bottom-width: 1px;

height: 210px;
}


.testo_desc
{
color: white;
font-family: arial;
font-size: 10pt;
text-align: center;
}


#menu
{
font-size: 10pt;
background: #fbe792;
color: black;
font-family: arial;
height: 50px;
vertical-align: middle;
}


#menu .coll:visited
{
color: black;
}


#menu .coll
{
color: black;
text-decoration: none;
}


#menu .coll:hover
{
color: red;
}


#banner_bottom
{
position: relative;
width: 100%;
height: 80px;
background: #f1c200;
float: left;
z-index: 1;
}


.titolo_box{ margin-left:20px;}
.testo-box{ margin:15px;}


.apri{ font-size:18px; font-family:Verdana, Geneva, sans-serif; margin-right:50px; text-align: center}
.apri:hover{ font-size:22px; font-family:Verdana, Geneva, sans-serif; cursorointer;}
.chiudi{ font-size:18px; color:#000; font-weight:bold; position:absolute; right:2%; top:0%; cursorointer;}






.overlay{
background:#000;
position:fixed;
top:0px;
bottom:0px;
left:0px;
right:0px;
z-index:100;
cursorointer;
/*Trasperenza cross browser*/
opacity: .7; filter: alpha(opacity=70);
-ms-filter:"progidXImageTransform.Microsoft.Alpha(Opacity=70)";

}




#box{ width:600px; height:400px; background-color:#FFF; display:none; z-index:+300; position:absolute; left:30%; top:20%; -moz-border-radius: 15px; -webkit-border-radius: 15px;
border-radius: 15px;}


#sin_prod .voce_categoria
{
font-size: 10pt;
font-family: arial;
text-decoration: none;
color: black;
}


#sin_prod .voce_categoria:hover
{
color: red;
}


#sin_prod .voce_categoria:visited
{
color: black;
}


#menu_top
{
position: relative;
float: left;
height: 110px;
margin-top: 3px;
width: 200px;

margin-left: 20px;

border-left-color: #647a77;
border-left-style: solid;
border-left-width: 1px;

border-right-color: #647a77;
border-right-style: solid;
border-right-width: 1px;

border-top-color: #647a77;
border-top-style: solid;
border-top-width: 1px;

border-bottom-color: #647a77;
border-bottom-style: solid;
border-bottom-width: 1px;
}


#identificacion_cliente
{
position: relative;
float: left;
height: 110px;
margin-top: 3px;
width: 250px;


margin-left: 300px;

border-left-color: #647a77;
border-left-style: solid;
border-left-width: 1px;

border-right-color: #647a77;
border-right-style: solid;
border-right-width: 1px;

border-top-color: #647a77;
border-top-style: solid;
border-top-width: 1px;

border-bottom-color: #647a77;
border-bottom-style: solid;
border-bottom-width: 1px;
}


.area_distribuidor
{
color: black;
text-decoration: none;
}


.area_distribuidor:hover
{
color: red;
}


.area_distribuidor: visited
{
color: black;
}


#titolo_prodotti
{
text-align: center;
font-size: 12pt;
font-family: arial;
margin-top: 3px;
}


#menu_cli
{
font-size: 9pt;
font-family: arial;
}


#menu_cli ul
{
margin-top: 10px;
list-style-type:none;
margin-left: -10px;
}


#menu_cli ul li
{
margin-bottom: 3px;
}




#nuovo_utente table
{
margin-top: 10px;
font-family: arial;
font-size: 10pt;
/*border-left-color: #647a77;
border-left-style: solid;
border-left-width: 1px;

border-right-color: #647a77;
border-right-style: solid;
border-right-width: 1px;

border-top-color: #647a77;
border-top-style: solid;
border-top-width: 1px;

border-bottom-color: #647a77;
border-bottom-style: solid;
border-bottom-width: 1px;*/

background: url('../images/sfondo_formulario.png') no-repeat;
}


.link_reg
{
color: black;
text-decoration: none
}


.link_reg:hover
{
color: red;
}


.link_reg:visited
{
color: black;
}


.tab_anteprima
{
margin-top: 0px;
font-family: arial;
font-size: 10pt;
/*border-left-color: #647a77;
}

#tab_final
{
margin-top: 0px;
font-family: arial;
font-size: 10pt;
/*border-left-color: black;
border-left-style: solid;
border-left-width: 1px;

border-right-color: black;
border-right-style: solid;
border-right-width: 1px;

border-top-color: black;
border-top-style: solid;
border-top-width: 1px;

border-bottom-color: black;
border-bottom-style: solid;
border-bottom-width: 1px;*/
}

.forma_pago
{
margin-top: 0px;
margin-bottom: 10px;
border-left-color: black;
border-left-style: solid;
border-left-width: 1px;

border-right-color: black;
border-right-style: solid;
border-right-width: 1px;

border-top-color: black;
border-top-style: solid;
border-top-width: 1px;

border-bottom-color: black;
border-bottom-style: solid;
border-bottom-width: 1px;
}


.titolo_box{ margin-left:20px;}
.testo-box{ margin:15px;}


.apri2{ font-size:10pt; font-family:arial; margin-right:0px; text-align: center; text-decoration: none}
.apri2:hover{ font-size:10pt; font-family:arial; cursorointer;}
.chiudi2{ font-size:18px; color:#000; font-weight:bold; position:absolute; right:2%; top:0%; cursorointer;}






.overlay2{
background:#000;
position:fixed;
top:0px;
bottom:0px;
left:0px;
right:0px;
z-index:100;
cursorointer;
/*Trasperenza cross browser*/
opacity: .7; filter: alpha(opacity=70);
-ms-filter:"progidXImageTransform.Microsoft.Alpha(Opacity=70)";

}
#box2{ width:600px; height:400px; background-color:#FFF; display:none; z-index:+300; position:absolute; left:30%; top:20%; -moz-border-radius: 15px; -webkit-border-radius: 15px;
border-radius: 15px; overflow: Auto;}

--------------HTML/PHP---------------
<head>
<link href="css/stile.css" rel="stylesheet" type="text/css" />
</head>
<?
include 'conf/connect.php';
?>


<body>
<div>
<?
include 'top.php';?>
</div>
<div>
<?
include 'menu.php';
?>
</div>

</body>

se hai bisogno anche dei contenuti delle pagine php fammelo sapere così lo posto.

Grazie mille!!!