These days virtually all Web surfers use fairly modern CSS-aware Web browsers. Some may differ slightly in how they interpret the details of some formatting instructions, but they all present CSS-formatted type in at least roughly the same way.
CSS type formatting covers a range of useful controls, from specific type sizes and separate word and letter spacing this was actually a step beyond QuarkXPress until recently) to leading, first line indents and inter-paragraph spacing. It is more complex to write, but then the majority of today’s Websites are put together with tools such as Dreamweaver, Freeway or GoLive, tools which help produce complex code automatically. However even if you never write a line of CSS code yourself it is well worth understanding what it can and can’t do, so you’ll understand the limitations when considering future productions.