Centering AlwaysVisibleControl?

I'm using an update progress control inside of an always visible control to communicate to users when my application is loading data. I want to center the control on the screen but have seen no way by which to do this. Has anyone figured out a way to position the AVC in the center of the browser screen? Is there a better way to do this?

In the html for your panel you define an outer div with width and height set to 100%, a transparent background and text centered. An inner div is set with a solid background and the top attrib set to 50% or some offset. The inner div will then be centered within the outer div.