CSS
From Official XMG Wiki
CSS is a great way to manage your website design. Once you've learned HTML, CSS is the next step. While you can manage to get by on HTML alone, CSS can help you by :
- Saving you time.
- Saving you headaches.
- Impressing your friends at parties (Because even most programmers don't fool with CSS).
- Making your websites all "pretty". (or pretty lame, depending on your skill).