Good answers so far. Like John mentioned, the CSS wouldn't have any effect on SEO, doesn't even look at what's actually in the .css file (something to keep in mind when using css background images if the image is actually contextual).

As Dave said, both CSS3 and HTML5 are still getting developed, and validating an HTML5 document on [http://validator.w3.org/][1] even gives you a disclaimer in the results:

The validator checked your document with an experimental feature: HTML5 Conformance Checker. This feature has been made available for your convenience, but be aware that it may be unreliable, or not perfectly up to date with the latest development of some cutting-edge technologies. If you find any issues with this feature, please report them. Thank you.

To get some of the attributes you're going after with the CSS, you'd have to use the vendor extentions to get them working correctly, and if they're detected you'll automatically fail the validation, unless I'm mistaken. [1]: http://validator.w3.org/

Good answers so far. Like John mentioned, the CSS wouldn't have any effect on SEO, doesn't even look at what's actually in the .css file (something to keep in mind when using css background images if the image is actually contextual).

As Dave said, both CSS3 and HTML5 are still getting developed, and validating an HTML5 document on http://validator.w3.org/ even gives you a disclaimer in the results:

The validator checked your document with an experimental feature: HTML5 Conformance Checker. This feature has been made available for your convenience, but be aware that it may be unreliable, or not perfectly up to date with the latest development of some cutting-edge technologies. If you find any issues with this feature, please report them. Thank you.

To get some of the attributes you're going after with the CSS, you'd have to use the vendor extentions to get them working correctly, and if they're detected you'll automatically fail the validation, unless I'm mistaken.