Force div to be topmost element of any and all webpages

I’m currently building an open-source plugin for Chrome. It’s pretty far done — but there’s a couple bugs I’m trying to sort out. Essentially, a div (injected into a page’s HTML) that moves throughout any and all webpages needs to be the topmost element so that it’s visible. This is achieved by z-index @ 999. On some webpages however, this doesn’t work!

Off the top of my head, the menu bar when you’re logged in at code.google.com overlays my div.

How do I force it to be the topmost when injected no matter what a web developer does?

Here’s my CSS for the div:

#ezselected {
  -webkit-transition: all .2s ease-in-out;
  -moz-transition: all .2s ease-in-out;
  -o-transition: all .2s ease-in-out;
  -ms-transition: all .2s ease-in-out;
  transition: all .2s ease-in-out;
  position:absolute;
  border-radius: 15px;
  z-index: 999;
  -webkit-box-shadow: 0px 0px 15px 5px rgba(255, 255, 100, .80);
  -moz-box-shadow: 0px 0px 15px 5px rgba(255, 255, 100, .80);
  /*box-shadow: 0px 0px 15px 5px rgba(255, 255, 100, .80);*/
  pointer-events:none; /* Make click-able through the DIV (for example, if it's on top of something with an event with kb) */
}

P.S., I tried !important to no avail.

Thanks!