Jquery date picker is showing behind popup window

When I click on text field available in pop window, the date picker calender is showing behind that popup window. Code for date picker initialization is

$("#nextSubmitDate").datepicker({
    changeMonth : true,
    changeYear : true,
    zIndex: 999999,
    position:"relative",
    dateFormat : "mm/dd/yy"
});

and code for popup window initialization is

var myPopup = new YAHOO.widget.Dialog("my-popup", {
    modal : true,
    visible : false,
    fixedcenter : true,
    constraintoviewport : true,
    underlay : "matte",
    width : "590px",
    height : "470px",
    zIndex: 200,
    autofillheight : "none",
    draggable : true,
    close : false
});

JSFiddle: http://jsfiddle.net/muyp84hs

I am using zIndex also after researching , even it is not working. Help me out where I am going wrong.

    .ui-datepicker 
{
 z-index: 9999 !important; 
}

after adding this code in my css , it is working fine.