Hi,

I have a popup panel in my page.

My page is placed under a master page with 960px width.

However, when i trying to open the popup panel in IE9, the greyed background seems will auto fit to the page size.

Chrome(working fine):

IE9(having problem):

*.aspx:

<asp:Button ID="Button1" runat="server" Text="Button" />
<ajaxToolkit:ModalPopupExtender ID="Button1_ModalPopupExtender" runat="server"
BackgroundCssClass="modalBackground" DynamicServicePath="" Enabled="True"
PopupControlID="Panel1" TargetControlID="Button1" RepositionMode="RepositionOnWindowResizeAndScroll" ViewStateMode="Inherit" CacheDynamicResults="True" ClientIDMode="AutoID">
</ajaxToolkit:ModalPopupExtender>
<asp:Panel ID="Panel1" runat="server" Width="1200px">
This is popup panel!</asp:Panel>

CSS:

.modalBackground
{
background-color: #000000;
filter: alpha(opacity=40);
opacity: 0.4;
-moz-opacity: 0.4;
}

//Content part in master page

#mainContent
{
padding: 20px;
width: 940px;
border-width: thin;
border-color: #ADB0CD;
position: relative;
height: 100%;
background-color: #FFFFFF;
box-shadow: inset 3px 3px 3px #CCCCCC, inset -1px -5px 5px #999999, 1px 2px 1px black;
-o-box-shadow: inset 3px 3px 3px #CCCCCC, inset -1px -5px 5px #999999, 1px 2px 1px black;
-webkit-box-shadow: inset 3px 3px 3px #CCCCCC, inset -1px -5px 5px #999999, 1px 2px 1px black;
-moz-box-shadow: inset 3px 3px 3px #CCCCCC, inset -1px -5px 5px #999999, 1px 2px 1px black;
-moz-border-radius: 10px 10px 10px 10px;
border-radius: 10px 10px 10px 10px;
overflow:auto;
line-height:20px;
}

Besides, any way to freeze the background when popup panel is display?