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Sure, CSS makes content look good with font changes, backgrounds, and all the rest, but what about accomplishing basic layout tasks? Enter floating and positioning. These are the tools by which you can set up columnar layout, overlap one piece of layout with another, and generally accomplish everything that so many tables have been used for over the years.
The idea behind positioning is fairly simple. It allows you to define exactly where element boxes will appear relative to where they would ordinarily be—or relative to a parent element, another element, or even to the browser window itself. The power of this feature is both obvious and surprising. It shouldn't shock you to learn that user agents support this element of CSS2 better than many others.