cosi' su Chrome 43.0.2357.81 ed IE 11 mi funziona

codice:
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <style>
        .tBold
        {
            font-weight:bold;
        }


    </style>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <asp:TextBox ID="tb1" runat="server" CssClass="tBold" Text="Ciaoooo"></asp:TextBox>
    </div>
    </form>
</body>
</html>