[Débutant] asp.net page center screen

bonjour
j'ai utilisé ce code pour centrer ma page :

CSS :

Code:

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body 
{
	text-align:center;
}
.wrap
{
	width:500px;
    margin-left:auto;
    margin-right:auto;
    text-align:left;
}

et mon code HTML :

Code:

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<%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPage.master.cs" Inherits="MasterPage" %>
 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Pagina senza titolo</title>
    <asp:ContentPlaceHolder id="head" runat="server">
    </asp:ContentPlaceHolder>
    <link href="StyleSheet.css" rel="stylesheet" type="text/css" />
</head>
<body>
    <form id="form1" runat="server">
         <div id="wrap">
        <asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">
 
 
 
        </asp:ContentPlaceHolder>
        </div>   
    </form>
</body>
</html>

ou est l'erreur ?

merci