CSS Perfomance Testing
Written by Jon Skypes wrote up a CSS performance test across browsers comparing CSS styling by no styling, by tag, by class, by descender, and by child. While for most cases everything seems pretty close as far as Safari and Firefox goes and of course IE is a whole lot slower. In real world applications you would never really have that many styles in your style sheet so in most cases I don’t think you would see a difference in speed. It is interesting to note as these web applications become more and more complex this may be an issue. As of right now I think we’re pretty far off before we need to worry about it.