How is can css be used in SEO?

Question

At first I thought css was used for absolutely nothing but styling the document when the user viewed it in a browser. But then I realized that css is also used by search engines in indexing pages. Search engines don't index content with display: hidden I believe, and heavily penalize sites that use keyword stacking (text that is never seen by the user, either the same color as its background or that appears far off the screen).

Are my 2 assumptions correct? How else is CSS used by search engines?

Answer 1

Yes you are right. Do a quick search on google with the keywords SEO and CSS and you'll find plenty of articles like this one:

http://www.stonetemple.com/articles/css-and-seo.shtml

Answer 2

In general, your assumptions are correct. If the text cannot be seen by the user, then it is not meaningful text, and therefore it is not indexed. In the past, webmasters would game the system by putting irrelevant keywords and text in their pages and hiding it, in an attempt to get illegitimate search engine hits.

In addition, use of headings such as H1 and the positioning of the text on the page (which can be affected by CSS) has an influence on search ratings.