CSS Pseudo-classes
Pseudo-class are an interesting group of selectors in CSS that apply to elements when they're in a certain state or condition. The most prevalent use of pseudo classes is to style the various states of text links.

Custom scrollbar colors
In IE5.5+ and above, you can use CSS to customize the color of the scrollbars on the page, which includes various components of the scrollbar. This example shows you the code.

CSS Generated Content
CSS2 supports the insertion of generated content, which is content that's specified using your style sheet and applied dynamically to the page according to your CSS definition. This is very useful for further decorating an element with rich content that should not be part of the page's actual markup.