Cascading Style Sheets (CSS) save bandwidth, vastly reducing the size of your files . With styles, your sites load faster. You work faster, too. Styles shave grueling hours of grunt-work off your design workload: one brief CSS document can style an entire domain; and when it’s time to redesign, you can execute site-wide changes in minutes instead of days.
Why learn something you don't need? Seeing as style sheets offer so much more power and flexibility, and now that style sheets are supported on virtually every browser around, it doesn't make sense to waste time with something you'll outgrow anyways.
As a basic rule of thumb, you can count on good all-around CSS support in Netscape Navigator 6, Internet Explorer 5 for Windows, Internet Explorer 4.5 for Macintosh, Opera 3.6, and any version of Firefox or Safari. In later browser versions, the support just gets stronger.