If you've made a website lately, you've used CSS. If you've used CSS there's probably a head-sized dent in the wall near your desk! Sass is an amazingly useful CSS pre-processor that brings a suite of programmatic tools such as variables, operators and functions to your CSS. It helps you keep your style code tidy and dry by letting you nest styles inside the selectors to which they apply, and break your styles into logically organized partial files among other wonders. Sass is a powerful tool, meaning if you're not careful it can help you to implement bad choices on a huge scale, so we'll also cover how to use CSS and Sass responsibly.