Question about theme Z-Index

Is there some sort of jQuery or CSS that controls a master theme z-index? I am trying to get a popup form working, and no matter what I do I cannot get the z-index working correctly. On a static HTML site on my PC it is working fine.

Here is the demo: http://www.buzzusborne.com/button/

Here is my demo page: https://www.virginiaseo.org/canvas-tester/

I have changed the z-index of #header as well as the modal dialog and backdrop generated from the popup plugin.

Here is the backdrop:

.modal-backdrop {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index: 100;
  background-color: #373c44;
}

Here is the modal:

.modal {
  text-align: left;
  position: fixed;
  top: 50%;
  left: 50%;
  z-index: 200;
  width: 398px;
  margin: -17% 0 0 -250px;
  background-color: #FFF;
  z-index: 1000;
  -khtml-border-radius: 3px;
  -moz-border-radius: 3px;
  -webkit-border-radius: 3px;
  border-radius: 3px;
  box-shadow: 0 0 0 4px rgba(55, 60, 65, 0.1);
  -moz-box-shadow: 0 0 0 4px rgba(55, 60, 65, 0.1);
  -webkit-box-shadow: 0 0 0 4px rgba(55, 60, 65, 0.1);
  padding: 50px 50px 55px;
}

This is not pressing, as it is only an experiment with Campaign Monitor email sign up.