jQuery UI-防止对话框拖动到div上方

有没有办法防止jQueryUI对话框在上面或下面出现 #top #顶

有什么建议吗?

HTML:

<div id="top"></div>
<div id="dialog">My dialog</div>

JS:

$(document).ready(function() {
    jQuery("#dialog").dialog({
                            autoOpen:true,
                            modal: false,
                            resizable: true,
                            draggable: true,
                            closeOnEscape: true,
                            title: "Title",
        open: function(){
            jQuery('.ui-widget-overlay').bind('click',function(){
                jQuery('#dialog').dialog('close');
            })
        }
    });
});

https://jsfiddle.net/9gku6qrh/