Why JQuery dialog goes slightly outside the main window when in maximized mode

When i open Jquery dialog in maximized mode using $(window).width() & $(window).height() or $(document).width() & $(document).height(). It slightly goes out of main window. My Jquery code is:

function DisableBackGrd() {
        var dlg = $("#divCreateInqGeneral").dialog({ bgiframe: true,
            width: $(window).width(),
            height: $(window).height(),
            modal: true,
            resizable: false,
            focus: function () { hideScrollBars(); },
            open: function () { hideScrollBars(); },
            beforeClose: function () { showScrollBars(); }
        });
        dlg.parent().appendTo(jQuery("form:first"));
    }

Relevant HTML

<div id="divCreateInqGeneral" styl开发者_如何学JAVAe="display: none">
    <uc1:CreateInqGeneral ID="Tab1UCCreateInqGeneral" runat="server" />
</div>

I found something here:

var theDialog = $(".mydialog").dialog({
    autoOpen: false,
    resizable: false,
    modal: true,
    width:'auto'

});

Bind an event in window.resize like this:

$(window).resize(){
//Resize height/width of your dialog here
}