CSS preprocessors are extension languages that compile into CSS. They add functionalities to CSS such as variables, mixins and nested inheritance. The added features depend on that specific preprocessor.
CSS preprocessors result in cleaner, easier to read code that’s faster to edit than pure CSS. Another major benefit is that preprocessors feature ways to write reusable code blocks, helping developers adhere to the principle of DRY (don’t repeat yourself) programming. CSS postprocessors parse plain CSS (for example: to include vendor prefixes).
When choosing the best option for your project, consider the community. A large, active community will make it easier to get support and will provide more learning resources.
Consider how detailed and well-written the documentation is. Is the information organized well and are enough examples provided? Check to see if it’s actively developed for bug fixes and new features.