Does Google Read Your CSS Files?
In the past, everyone knew that Google and the other engines, stayed away from your CSS files. However, after on October 19th, Matt Cutts posted a blog entry named SEO Mistakes: Unwise comments which showed an example of someone using CSS. Matt wrote;
I don’t recommend that people use CSS to hide text, and I don’t recommend that they document it, either.
Then Jagger update hit us, and many now believe that Google does peak at your CSS files. A DigitalPoint Forum thread asks Does google read external CSS files yet? Some reply "no" right off the bat, but I wouldn't be so quick to say no. Many respectable SEOs have been chattering about Google reading your CSS just for this. So just be careful, especially now.
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rustybrick in Google Optimization at November 11, 2005 8:53 AM
Comments (11)

Comments
I don't have a DP account, so I'll post this here.
First off, there are only two ways Google would be able to tell whether you are using CSS to hide information:
One, they spider the page with a CSS-enabled bot, scrape the visible content and do a word count, and then spider the page a second time with CSS-disabled bot, scrape the visible content, and do another word count, and finally do a word-count-comparison.
Or...
They simply read the external CSS file, which would take a heck of a lot less work, processing power, bandwidth, etc.
The problem with the second option is almost as great as the first. There are *many* differrent techniques that can be used to hide content, whether for good or for evil. Display: none is easy, but what about using text-indent and overflow: hidden? Or simply including an extra span, and then placing the span *over* the content? Or zeroing out the height of the element? Etc., etc., etc., and so on and so forth. And again, these techniques can be used to deliver a much more user-rich experience, or to try and trick a search-engine.
Either way, I don't think Google is dumb enough to start penalizing sites based on their CSS techniques alone. More likely, they can just continue to ignore the CSS files, and concentrate instead on the content of the page. Too much hidden content is going to raise a keyword-spamming flag, since the content is still there on the page. Pages that don't raise such a flag may get included, only to be reported using Google's "Report a Spam Result" page.
In short, though CSS *might* be used to game the search engines, it can't be used to stop a site from being penalized, excluded, etc., due to the regular spam-result detection Google is constantly working to improve.
Posted by Blair at November 11, 2005 11:03