The only "error" is the British English way of spelling grey.
I surprised that all browsers still understand the meaning of "gray" as opposed to "grey". Anyway, it's fixed. The CSS validates now.
Or is it the other way around. Whatever. I'm Indian, so I grew up under the shadow of the British Monarchy, coupled with the modernism "invasion" of the 'Mericans. That's fucked up English for you. More fucked up than the Brits or the Americans. Did you read the text on the site, by the way? Took me half an hour to write.