Sass is a preprocessor scripting language that is interpreted or compiled into Cascading Style Sheets. SassScript is the scripting language itself. Sass consists of two syntaxes.
Less is a dynamic preprocessor style sheet language that can be compiled into Cascading Style Sheets and run on the client side or server side.
Stylus is a dynamic stylesheet preprocessor language that is compiled into Cascading Style Sheets (CSS). Its design is influenced by Sass and LESS. It's regarded as the fourth most used CSS preprocessor syntax
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