What is CSS?
CSS is a style sheet used to separate the syntax from the semantics of a web page. When html was first created, tags not only defined what an element was, but also defined what it looked like. If a large site wanted to changed how the different pages looked, the html programmer would have to go to each and every tag in every page to change the look. CSS files changed that. CSS are used to define various properties of the various elements in a web page. So now, instead of having to change all tags, you can just change to properties in the CSS file. This makes web design much simpler.
Here are some examples of CSS: