Pure CSS offers a minimalist, mobile-first approach to CSS layouts in your web pages. Let's get started with this lightweight framework, which you can use as-is or extend with a variety of plugins.

Ryan Boudreaux covers the basics about CSS specificity hierarchy in an effort to make this tricky concept easier to understand.

Your actual CSS classes will probably define other attributes such as font-family, border-style, margin or width. Override them using the same technique you used to make the DIV's background color ...