Sass is a CSS pre-processor. Sass reduces repetition of CSS and therefore saves time.
Sass lets you use features that do not exist in CSS, like variables, nested rules, mixins, imports, inheritance, built-in functions, and other stuff.
Read more about Sass at the official Sass web site: https://sass-lang.com/
Sass Syntax https://sass-lang.com/documentation/syntax
Sass supports two different syntaxes. Each one can load the other, so it’s up to you and your team which one to choose https://sass-lang.com/documentation/syntax