Adding inner shadow to thumbnails?

This might be more of a CSS thing, but as far as I know this should work, so it might be something the NextGen Gallery is doing…

I’m trying to ad an inner shadow to my thumbnails be adjusting the default css in this way:

.ngg-gallery-thumbnail img {
	display:block;
	position:relative;
	margin: 0 22px 22px 0;
	-moz-box-shadow:inset 0 0 10px #000000;
	-webkit-box-shadow:inset 0 0 10px #000000;
	box-shadow:inset 0 0 10px #000000;
	z-index: 99;
}

The new part being:

-moz-box-shadow:inset 0 0 10px #000000;
	-webkit-box-shadow:inset 0 0 10px #000000;
	box-shadow:inset 0 0 10px #000000;
	z-index: 99;

It works fine, except that the shadow box shows up UNDER the thumb IMG, I figured this would be a simple z-index fix, but it doesn’t seem to matter how high I go with that, it still has the IMG sit on top fo the shadow box.

Any advice? you can see the page I’m working on here:
http://tcurranmusic.com/new/gallery/

Thanks!