CSS

CSS

Whereas HTML was the basic structure of your website, CSS is what gives your entire website its style. Those slick colors, interesting fonts, and background images? All thanks to CSS. It affects the entire mood and tone of a web page, making it an incredibly powerful tool -- and an important skill for web developers to learn. It's also what allows websites to adapt to different screen sizes and device types.
To show you what CSS does to a website, look at the following two screenshots. The first screenshot is one of my colleague's blog posts in Basic HTML, and the second screenshot is that same blog post with HTML and CSS.

Put simply, CSS is a list of rules that can assign different properties to HTML tags, either specified to single tags, multiple tags, an entire document, or multiple documents. It exists because, as design elements like fonts and colors were developed, web designers had a lot of trouble adapting HTML to these new features.
You see, HTML, developed back in 1990, was not really intended to show any physical formatting information. It was originally meant only to define a document's structural content, like headers versus paragraphs. HTML outgrew these new design features, and CSS was invented and released in 1996: All formatting could be removed from HTML documents and stored in separate CSS (.css) files.
So, what exactly does CSS stand for? It stands for Cascading Style Sheets -- and "style sheet" refers to the document itself. Ever web browser has a default style sheet, so every web page out there is affected by at least one style sheet -- the default style sheet of whatever browser the web page visitor is using -- regardless whether or not the web designer applies any styles. For example, my browser's default font style is Times New Roman, size 12, so if I visited a web page where the designer didn't apply a style sheet of their own, I would see the web page in Times New Roman, size 12.

Obviously, the vast majority of web pages I visit don't use Times New Roman, size 12 -- that's because the web designers behind those pages started out with a default style sheet that had a default font style, and then they overrode my browser's defaults with custom CSS. That's where the word "cascading" comes into play. Think about a waterfall -- as water cascades down the fall, it hits all the rocks on the way down, but only the rocks at the bottom affect where it will end up flowing. In the same way, the last defined style sheet informs my browser which instructions have precedence.
To learn the specifics of coding in CSS, I'll point you again to the free classes and resources on code academy. But for now, let's talk a bit about JavaScript.