correcting validation errors

Site URL: http://www.perthpunk.com
(Twenty Twelve child theme)

Hi folks. I’m trying to work my way through correcting some of the validation errors on my site.

eg: Here’s one I can’t figure out:

URI : http://www.perthpunk.com/wp-content/themes/twentytwelve/style.css
(257)
.menu-toggle, input[type=”submit”], input[type=”button”], input[type=”reset”], article.post-password-required input[type=”submit”], .bypostauthor cite span

Value Error : background-image top is not a color value

Could someone please explain this? It seems to be some error in the Twenty Twelve parent stylesheet – should I be messing around with that to “correct” it? And how would I correct this error, anyway?

I have several other such errors, so if I know how to fix this one, I should be able to apply that knowledge to the others.

Cheers
Ross