SASS

While CSS is a great language, it’s very basic. It lacks some useful and common functionality found in other (programming) languages. For example, you cannot nest selectors, or reuse variables.

To solve this problem, SASS was invented. It’s a pre-processor: after typing your code, it will process it, and convert it to a regular CSS file.

I cannot recommend using a CSS pre-processor enough. It’s a simple layer on top of CSS, easy to learn, and has only advantages.