Sass

Sass (which stands for 'Syntactically awesome style sheets) is an extension of CSS that enables you to use things like variables, nested rules, inline imports and more. It also helps to keep things organised and allows you to create style sheets faster.
Sass is compatible with all versions of CSS. The only requirement for using it is that you must have Ruby installed. Sass is CSS compatible & with Sass you can - organize large Stylesheets, use its features such as Nesting, Variables, Loops, Arguments, etc.