Oddly enough the browser which most accurately renders all CSS codes at this time is the 3.5x version of upstart Opera. Features like background formatting and box positioning are still supported inconsistently enough for wary designers to want to avoid them, the more basic text formatting is strong enough to inspire you to take the plunge. The goal of CSS is to provide a way of separating content from formatting. The idea is to enable designers to use Heading tags and List elements again without having to sacrifice aesthetic control. Chances are you've probably formatted your page titles to stand out from the regular body text.
Most sites use different fonts in a larger size with a unique color for title text.
And sites achieve this look by using the tag for each and every page title. CSS allows you instead to put your title text back into a H1 tag where it belongs structurally and then define the H1 tag so that your titles appear with the exact font, size and color that you want. A few older browsers won't recognize the style sheet and will resort to their default settings in order to render the H1 tag but most will never know the difference. The real payoff comes down the line when you start creating different style sheets for different viewers. Combining browser detection with style sheets allows you to tailor your web site to individual browser needs without having to ever retouch the content.