CSS: Cascading Style Sheets
So, basically, CSS is what allows me to give different looks to different sites on my page. For example, the text on this page black while the text on my About page is white. This was done using CSS. This text is in a different font. Guess what, that's CSS. As you can see, CSS is a very useful tool in creating websites that actually look interesting. The adaptive navigation bar on the top of this page is made with CSS with the added magic of Bootstrap.