The original implementation had the overlays just change the border color when

hovering over them to drop. This wasn't a particularly noticible transition,

especially given the other colors we use on the page. This change switches that

over to just lightening the background color instead.
While I was doing this, I also fixed the code to cope with padding, which was

an issue on the file attachments overlay when there were existing file

attachment thumbnails present.

Did some drops.