CSS to format specific rel= relationships ?

Hello! I was wondering if there was a standard’s compliant way to style links differently based on their rel="attribute" ?

For example, I use lightbox to display some of the images on my site; I would like to have links to those images styled differently than my other links. From what I know now, I could do a:

a[href$=".png"] { background: url('linkimage.gif'); }

However, because I already have to signify my links with a rel="lightbox", I thought that might be a better way to gaurantee that all the links to images with the correct rel= tag would have the little image next to them.

Can I do that? Thanks!