Popup Shows Behind header content

I’m in the process of setting up a gallery on my site and have loaded two test images. When I click on the image, it loads in the lightbox but appears behind the header. I cant seem to figure out what edit I need to make in the css. Any assistance is helpful. Thanks. I’ve tested it on Chrome and Firefox and get the same issue. Thanks

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