Media Grid content element gray boxes

I used a Content Element Media Grid to display images on my site. On the on the large image view, when you click on an image, there is a translucent gray box covering half the image, which shifts to the other side of the image as you mouse over it. The gray box goes away when the cursor is off the image. How can I get rid of that shifting gray box?

http://www.stoddardesign.com
Thanks for your help.