Have you ever read a script for a play? It's not nearly as fun as seeing it performed. Thanks to CSS, or Cascading Style Sheets, all the world's a stage! CSS takes the original script and brings it to life in full color, exactly how it should be. CSS builds the set, designs the lighting, and gives a perfect performance every time.
So CSS is how you experience the content, it's the presentation! The separation between content and presentation allows for increased accessibility, flexibility, and control over specific characteristics. Actors could not put on a worldclass performance if they still needed to read off their scripts! Want to see Romeo and Juliet in Los Angeles instead of fair Verona or to present any content differently? Everything you need is isolated in CSS and you can get what you want if you just use a separate style sheet!
But what does "Cascading" mean? Is it because CSS's founders, Hakon Wium Lie & Bert Bos, loved the Cascade Mountains?
No, definitely not. They were both in Europe when CSS was released in 1996 and weren't big climbers.
Cascading in this context refers to the way the code determines which rule to apply if there are multiple rules effecting the same element. It makes that decision through a predictable, cascading, priority scheme. Here, cascading means that the order of the code is important, and has downstream effects. And what about a priority scheme? Well, a priority scheme is just a fancy way to say that some things are more important, or prioritized and ordered, before other things. This cascading effect allows for multiple style sheets to be used on one HTML document.