What is a CSS pre-processor?
A pre-processor is a program that processes its input data to produce output that is used as input to another program.
A CSS pre-processor will allow writing clean CSS in a programming construct instead of static rules and it will output the result in clean CSS.
Google provides a few notes about DevTools and working with CSS pre-processors.
For the cons of using pre-processors, check out Miller Medeiros‘ blog post.
Finally, here’s an epic YouTube Playlist on SASS related topics: