[subrc]

I noticed this as well a while back, and changed our "CSS" link in our footer like you did. Turned out our stylesheet still had some errors in it thanks to normalize.css. I'm not too bothered by it though, and here's why.

There's technically no accessibility benefit to using completely valid CSS. CSS is just a presentation tool after all. Valid HTML is important because it allows your website to target browsers which you don't usually think about, such as search engines and screen readers. Valid CSS doesn't let you do this.

I have a hard time thinking you need to worry about whether you get errors for using vendor extensions in your CSS. Or about whether or not you are using hacks in your CSS, for that matter.

So right now, our website doesn't have valid CSS, and I'm not too bothered to change that. I'd love for someone to prove me wrong here and get me to fix that.