Is W3C invalid HTML and CSS code harmful for SEO and problematic for screen reader users?

Question

If i made a site and site looking well in all a grade browsers but if site shows some errors in both XHTML and CSS validation then is there any benefit to solve those errors?

Is site with 10 validation errors better than site with 35 validation errors or both are same for search engine?

Does search engine read css file? Does CSS validation has any importance for SEO?

Answer 1

That depends on the kind and place of errors, I guess.

If these make your site semantic structure undecipherable then, yes, sure they will be a problem for any automatic analysis tool.

If these are non-standard attributes (or incorrect attribute values) then they won't.

Answer 2

Quite simply invalid XHTML is lazy; there are a million ways to ensure your XHTML is valid. We have standards for a reason and ensuring your XHTML is valid means it can also be read by XML parsers and therefore consumed by future web applications and comparison sites. For me, ensuring your mark-up is valid is always worth the extra investment.

I also believe Google parse CSS files in order to detect black hat SEO tricks such as white text on a white background. I understand many people think it's a step too far for the Google bots but keep in mind, Google has the entire chrome engine at its disposal. If I were Google and I suspected a site were potentially spammy, I would run it though my Chrome engine and look for CSS hacks.

Another indication Google parses your CSS is the new page speed tools provided by Google. This tool highlights potentially slow CSS selectors and recommends you amend them. As Page Speed is now a factor in determining Page Rank, it goes without saying Google is not only considering your total page size but render time too.

So, I would say... Don't be lazy ;)