Date behind popup

I have your plugin activated and working on a page – however, if I place the ContactForm7 form with the date/time picker into a popup window; the date selector container shows behind the popup.

I tried using css to set the z-index of it like this;
.xdsoft_datetimepicker {
z-index:500;
}
but that does not work. Is there a way to set it so that it shows “above” everything?

The page I need help with: [log in to see the link]