Can I use an attribute selector to add background images to text link and remove them from linked thumbnail images?

Can I use an attribute selector to add background images to text link and
remove them from linked thumbnail images?

I'm using an attribute selector to add a background icon (PDF, Word) to
the text links. I'm also using thumbnail images to link to the same
documents (PDF, Word). When using a thumbnail image, I don't want the
background icon (PDF, Word icon)showing up next to the linked thumbnail
image. Is there a way? There are no classes or ids.