Ah, great idea, multiple shadows What you posted looked great in chrome but was a bit rubbed out in Fx on the top ... I updated the test site with the following (and tweaked the position to close the lower right gap on big-ol-zooms)
box-shadow: 2px -2px 0 1px rgba(200, 204, 204, 0.7), 3px -3px 0 2px rgba(255, 255, 255, 0.1);