I display a gridview in a ModalPopupExtender. When the screen resolution is to small, the pop-up is to big to all be displayed on the page.

I just want to add scroll bar to the pop-up when this happen.

I know it's probably some CSS, but all I tried did not work.

here some base css

.modalTextBoxBackground
{
   background-color:Gray;
   filter:alpha(opacity=70);
   opacity:0.7;
}  
.modalTextBox
{
    border: 1px solid #FFFFFF;
    background-color: #0066CC;
    color: #00FFFF;

}

here some code from the aspx

<asp:Panel ID="OptionSelectionPanel" runat="server" CssClass="modalTextBox">
            <asp:UpdatePanel ID="OptionSelectionUpdatePanel" runat="server" UpdateMode="Conditional" >
            <Triggers>
                <asp:asyncPostBackTrigger ControlID="TemplateSelection" />
            </Triggers>
            <ContentTemplate>

            <table class="EditRow">
            <tr class="HeaderFooter">
            <td colspan="3" class="modalTextBoxTitle">
                Add options to Quote
            </td>
            </tr>
            <tr>
            <td>
                Manufacturer
            </td>
             <td>
                <asp:DropDownList ID="OptionManufacturerFilter" runat="server" 
                    DataSourceID="OptionManufacturerDataSource" DataTextField="Name" 
                    DataValueField="Code" AutoPostBack="True" >
                </asp:DropDownList>
            </td>
            </tr>

                            <tr>
            <td colspan="3">
                <asp:GridView ID="NewOptionSelection" 
                              runat="server" 
                              DataSourceID="AvailableOptions" 
                              DataKeyNames="Option_Id"
                              AllowPaging="True" 
                              AllowSorting="True" 
                              AutoGenerateColumns="false">
                <Columns>
                    <asp:BoundField DataField="category_Descr" HeaderText="Category" SortExpression="category_Descr,subcategory_Descr,code" />
                    <asp:BoundField DataField="subcategory_Descr" HeaderText="Sub-Category" SortExpression="subcategory_Descr,code" />
                    <asp:BoundField DataField="Manuf_Name" HeaderText="Manufacturer" SortExpression="Manuf_Name"/>
                </Columns></asp:GridView>
            </td>
            </tr>
            <tr class="HeaderFooter">
            <td colspan="3" class="Center">
                <asp:Button ID="OptionSelectionClose" runat="server" Text="Close" />

            </td>
            </tr>
            </table>
             </ContentTemplate>
            </asp:UpdatePanel>
        </asp:Panel>
       <asp:Button runat="server" ID="HiddenTargetControlForOptionSelectionModalPopup" style="display:none"/>    
        <cc1:ModalPopupExtender ID="OptionSelectionModalPopupExtender" runat="server" 
                                TargetControlID="HiddenTargetControlForOptionSelectionModalPopup"
                                PopupControlID="OptionSelectionPanel" 
                                BackgroundCssClass="modalTextBoxBackground" />