How to display ajax calender extender on top of modal popup extender?

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C#

ASP.NET

CSS

I have used Ajax Modal popup extender for popup an the css for modal popup is as folows:
I have visited most of website question but nothing seemed to have worked.
.modalBackground
{
-webkit-border-radius: 12px 12px 23px 23px;
border-radius: 12px 12px 23px 23px;
-webkit-box-shadow: 12px 12px 12px 0 #946C10;
box-shadow: 12px 12px 12px 0 #946C10;
background-color: LightGrey;
filter: alpha(opacity=80);
opacity: 0.7;
position:fixed;
}

and the HTML for modal popup is as shown bellow:

<cc1:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="btncomplains"
            PopupControlID="panelstatus" BackgroundCssClass="modalBackground" CancelControlID="ImageCancel1">
        </cc1:ModalPopupExtender>

<asp:Panel ID="panelstatus" GroupingText="Submit Details" BackColor="WhiteSmoke"
            Width="600px" runat="server" Style="border: thick solid #CCCCCC;">
            <div>
                <div align="right" style="padding: 2px; width: auto; height: 25px;">
                    <asp:Image ID="ImageCancel1" runat="server" ImageUrl="~/images/close2.png" CssClass="image_hover"
                        Width="25px" />
                </div>
                <asp:UpdatePanel ID="UpdatePanelpopup1" runat="server">
                    <ContentTemplate>
                        <table style="width: 580px">
                            <tr>
                                <td class="textalignment">
                                    <asp:Label ID="lblserialno" runat="server" Font-Bold="True" Text="Serial Number :"></asp:Label>
                                </td>
                                <td class="auto-style5">
                                    <asp:TextBox ID="txtserialno" runat="server" CssClass="textbox"></asp:TextBox>
                                </td>
                                <td class="tablealignmentcnlbtn">
                                    <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="txtserialno"
                                        ErrorMessage="Please Enter Serial No" ForeColor="#FF3300" ValidationGroup="process"
                                        Font-Size="Small"></asp:RequiredFieldValidator>
                                </td>
                            </tr>
                            <tr>
                                <td class="textalignment">
                                    <asp:Label ID="lblpinno" runat="server" Font-Bold="True" Text="Pin Number :"></asp:Label>
                                </td>
                                <td class="auto-style5">
                                    <asp:TextBox ID="txtpinno" runat="server" CssClass="textbox"></asp:TextBox>
                                </td>
                                <td class="tablealignment">
                                    <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="txtpinno"
                                        ErrorMessage="Please Enter Pin No" ForeColor="#FF3300" ValidationGroup="process"
                                        Font-Size="Small"></asp:RequiredFieldValidator>
                                </td>
                            </tr>
                            <tr>
                                <td class="textalignment">
                                    <asp:Label ID="lbltransactionid" runat="server" Font-Bold="True" Text="Transaction ID :"></asp:Label>
                                </td>
                                <td class="auto-style5">
                                    <asp:TextBox ID="txttransactionid" runat="server" CssClass="textbox"></asp:TextBox>
                                </td>
                                <td>
                                    <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="txttransactionid"
                                        ErrorMessage="Please Enter TransactionId" ForeColor="#FF3300" ValidationGroup="process"
                                        Font-Size="Small"></asp:RequiredFieldValidator>
                                </td>
                            </tr>
                            <tr>
                                <td class="textalignment">
                                    <asp:Label ID="lblrechargedate" runat="server" Font-Bold="True" Text="Recharge Date :"></asp:Label>
                                </td>
                                <td class="auto-style5">
                                    <asp:TextBox ID="txtrechargedate" runat="server" CssClass="textbox"></asp:TextBox>
                                    <cc1:TextBoxWatermarkExtender ID="txtrechargedate_TextBoxWatermarkExtender" runat="server" TargetControlID="txtrechargedate"   WatermarkText="MM/DD/YYYY" WatermarkCssClass="watermark">
                                    </cc1:TextBoxWatermarkExtender>
                                    <cc1:FilteredTextBoxExtender ID="txtrechargedate_FilteredTextBoxExtender" runat="server"
                                        FilterType="Custom,Numbers" TargetControlID="txtrechargedate" ValidChars="/">
                                    </cc1:FilteredTextBoxExtender>
                                    <cc1:CalendarExtender ID="txtrechargedate_CalendarExtender" runat="server" Enabled="True"
                                        TargetControlID="txtrechargedate" PopupPosition="BottomLeft">
                                    </cc1:CalendarExtender>
                                    <td class="tablealignment">
                                        <asp:RequiredFieldValidator ID="RequiredFieldValidator6" runat="server" ControlToValidate="txtrechargedate"
                                            ErrorMessage="*" Font-Size="Small" ForeColor="#FF3300" ValidationGroup="process"></asp:RequiredFieldValidator>
                                        <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ErrorMessage="Please Enter Date In (MM/DD/YYYY) format"
                                            ControlToValidate="txtrechargedate" ForeColor="#FF3300" ValidationExpression="^((((0[13578])|([13578])|(1[02]))[\/](([1-9])|([0-2][0-9])|(3[01])))|(((0[469])|([469])|(11))[\/](([1-9])|([0-2][0-9])|(30)))|((2|02)[\/](([1-9])|([0-2][0-9]))))[\/]\d{4}$|^\d{4}$"
                                            ValidationGroup="process" Font-Size="Small"></asp:RegularExpressionValidator>
                                    </td>
                            </tr>
                            <tr>
                                <td class="tablevalidation">
                                    &nbsp;
                                </td>
                                <td class="auto-style5">
                                    <asp:Button ID="btnpopsubmit" runat="server" CssClass="buttonsubmit" Font-Size="Medium"
                                        Height="40px" OnClick="btnpopsubmit_Click" Text="Submit" ValidationGroup="process"
                                        Width="100px" />
                                </td>
                                <td>
                                </td>
                            </tr>
                        </table>
                    </ContentTemplate>
                </asp:UpdatePanel>
            </div>
            <%-- </div>--%>
        </asp:Panel>

I have tried all sorts of z-index but nothing seem to have worked i have changed z-index from 0 to 99999999

and nothing have changed and so i resorted to required field validators and watermark but pls help me to show that on top of modal popup and pls tell me if i am doing anything wrong

I have also tried this script but didint worked:

script language="javascript" type="text/javascript">
         function onCalendarShown(sender,args)
         {
             alert(sender._popupBehavior._element.style.tostring());
             sender._popupBehavior._element.style.zIndex=9999999;

         }
         </script>

pls help!!