What is Sass? Sass is essentially CSS with superpowers. Sass is a preprocessor scripting language (SassScript) that is interpreted or compiled into Cascading Style Sheets. “Sass is the most mature, stable, and powerful professional grade CSS extension language in the world.” - sass-lang.com The difference between SCSS and Sass There are two syntaxes available for Sass. The first, known as SCSS (Sassy CSS) and used throughout this reference, is an extension of the syntax of CSS.