CKEditor maximize inside ModalPopupExtender - CSS Issue

Hey all,

I have a CKEditor inside a ModalPopupExtender which works fine. the problem exists when we maximize the CKEditor so it becomes full screen.
The thing is that our ModalPopupExtender has such CSS defined so that the background becomes a little bit grayed out so the user has the impression he can only work with the popup. Now when they maximize the CKEditor the entire screen remains gray and the editor is unclickable. How can I resolve this?

My code:

 <asp:Button ID="EditDescription_btnShowPopup" runat="server" Style="display: none" /> 
    <asp:Panel ID="EditDescription_pnlPopup" runat="server" Width="1200px" Height="800" 
        Style="display: none;"> 
        <asp:UpdatePanel ID="EditDescription_Modal_UpdatePanel" runat="server" UpdateMode="Conditional"> 
            <ContentTemplate> 
                <asp:Panel ID="Panel2" runat="server" Style="background-color: white; padding: 5px;"> 
                    <asp:HiddenField runat="server" ID="EditDescription_Modal_ArtID" /> 
                    <asp:Table runat="server" ID="EditDescription_ModalTable" Width="100%"> 
                        <asp:TableRow CssClass="td"> 
                            <asp:TableCell ColumnSpan="2"> 
                                <asp:Label runat="server" ID="EditDescription_LblTitle" Text="" BackColor="#B5C7DE" 
                                    Width="100%" Font-Bold="true" /> 
                            </asp:TableCell></asp:TableRow><asp:TableRow CssClass="td"> 
                            <asp:TableCell ColumnSpan="2"> 
                                    <CKEditor:CKEditorControl ID="CKEditorControl1" runat="server" Height="400" Width="1180" /> 
                            </asp:TableCell> 
 
</asp:TableRow> 
 
</asp:Table> 
 
</asp:Panel> 
 
</ContentTemplate> 
 
</asp:UpdatePanel> 
 
<div style="text-align: left"> 
            <asp:Button ID="EditDescription_btnSave" runat="server" Text="Save" Width="130px" 
                OnClientClick="GoToControlInHiddenField()" CausesValidation="true" ValidationGroup="EditDescription_Create" 
                OnClick="EditDescription_btnSave_Click" /> 
            <asp:Button ID="EditDescription_btnDummySave" runat="server" Text="DummySave" Style="display: none" /> 
            <asp:Button ID="EditDescription_btnCancel" runat="server" Text="Cancel" Width="70px" 
                OnClick="EditDescription_btnCancel_Click" /> 
        </div> 
    </asp:Panel> 
    <ajaxToolkit:ModalPopupExtender ID="EditDescription_mdlPopup" runat="server" TargetControlID="EditDescription_btnShowPopup" 
        PopupControlID="EditDescription_pnlPopup" CancelControlID="EditDescription_btnCancel" 
        BackgroundCssClass="modalBackground" OkControlID="EditDescription_btnDummySave" /> 

And the CSS of the ModalPopupExtender:

 .modalBackground 
{ 
    background-color: Gray; 
    filter: alpha(opacity=70); 
    opacity: 0.7; 
} 

Thanks in advance,
- Yannick