I've been struggling to figure out how to change the opacity of the prettyPhoto overlay. It's currently white (light_rounded theme), but I would like to be able see through it. I can't seem to find the correct code to change. Should this be done by altering the JS (jquery.prettyPhoto.js) or the CSS (prettyPhoto.css)? It might help if someone could show me the line of code I should be looking for...