加入ExtExtenders的ModalUpdateProgress 后页面不居中解决方案

UpdatePanel 配合ModalUpdateProgress 可以很好实现提交弹出模态遮罩层。可是遇到一个问题。就是加入了ModalUpdateProgress 。页面的不居中，反而偏左。
后来发现加了ModalUpdateProgress ，会自动给body加入一个CSS和ID属性。
解决方法是：在CSS文件加入来覆盖默认的样式。就搞定了。
#ext-gen6
{
 text-align: center;
 margin: 0 auto;
}


具体代码如下。

    <div>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="conditional">
            <ContentTemplate>
                <table cellspacing="0" cellpadding="0" width="100%" border="0">
                    <tbody>
                        <tr>
                            <td class="List_Left_t1">
                            </td>
                            <td class="List_t2" id="Td1">
                                用户登陆
                                <!--Title-->
                            </td>
                            <td class="List_t3">
                            </td>
                        </tr>
                    </tbody>
                </table>

                <table cellspacing="0" cellpadding="0" width="100%" border="0">
                    <tbody>
                        <tr>
                            <td class="List_m1">
                            </td>
                            <td class="List_m2" id="Td2">
                                <table cellspacing="0" cellpadding="0" width="100%" border="0">
                                    <tbody>
                                        <tr>
                                            <td class="ItemList" align="right" style=" 135px;">
                                                用户名：</td>
                                            <td class="ItemList">
                                                <asp:TextBox ID="txtName" runat="server" Width="150px"></asp:TextBox>
                                            </td>
                                        </tr>
                                        <tr>
                                            <td class="ItemList" align="right">
                                                密码：
                                            </td>
                                            <td class="ItemList">
                                                <asp:TextBox ID="txtPwd" runat="server" TextMode="Password" Width="150px"></asp:TextBox>
                                            </td>
                                        </tr>
                                        <tr>
                                            <td class="ItemList">
                                                &nbsp;
                                            </td>
                                            <td class="ItemList">
                                                <asp:Button ID="btn_Submit" runat="server" Text=" 登陆 " OnClick="btn_Submit_Click"
                                                    OnClientClick="javascript:return CheckForm()" />&nbsp;
                                                <asp:ImageButton ID="ImageButton1" runat="server" ImageUrl="~/App_Themes/Default/Images/mashangzhuce.jpg"
                                                    CausesValidation="false" OnClick="ImageButton1_Click" />
                                            </td>
                                        </tr>
                                    </tbody>
                                </table>
                            </td>
                            <td class="List_m3">
                            </td>
                        </tr>
                        <tr>
                            <td class="List_b1">
                            </td>
                            <td class="List_b2">
                                &nbsp;</td>
                            <td class="List_b3">
                            </td>
                        </tr>
                    </tbody>
                </table>
            </ContentTemplate>
        </asp:UpdatePanel>
        <ext:ModalUpdateProgress ID="ModalUpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1">
            <ProgressTemplate>
                <div>
                    处理中</div>
            </ProgressTemplate>
        </ext:ModalUpdateProgress>
    </div>