*CSS is a "new-Rave" Brazilian band from São Paulo - check them out on Wikipedia.
It's a tricky one to define if you've never built a website yourself and virtually impossible to talk about it without introducing yet more jargon. In short, if HTML defines the content of a webpage, CSS defines the look, feel and layout. If you use Word, think of it like the "styles" (Heading 1, Heading 2, Normal, etc.). If you take the time to set these up properly, it makes it much easier to globally control and update styles - just like CSS offers with websites.
In days gone by (thankfully), browser support for CSS was not particularly good. This meant you had a lot of inline formatting. Again, think of Word - instead of you simply selecting the text and clicking "Heading 2", you would have to define "Arial, 14pt, bold, black, underlined..." every time. Not very efficient...
You also had to use tables to define things like column layouts - tables are the curse of any HTML developer worth their salt! CSS not only allows you to define styles, it also lets you position items on a webpage - and it's the right way to do it.
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