Introduction
CSS has served us well for over a decade, but as web applications have grown more complex, the limitations of vanilla CSS have become increasingly apparent. Writing and maintaining large stylesheets is tedious and error-prone. We find ourselves repeating colors, copying similar rule sets, and manually calculating related values. The DRY (Don't Repeat Yourself) principle that we apply everywhere else in programming seems impossible to achieve with CSS.
Enter CSS preprocessors: tools that extend CSS with programming language features like variables, functions, and mixins. The two most popular preprocessors are Sass (Syntactically Awesome Stylesheets) and LESS (Leaner CSS). Both compile to standard CSS that browsers can understand, but they let you write more maintainable, flexible stylesheets during development.