Less

Less is a CSS preprocessor that extends the stylesheet language with dynamic features including variables, mixins, operations and functions. Developers use it to write more concise and maintainable stylesheets that compile down to standard CSS. The tool runs on both server-side environments with Node.js and client-side in modern browsers. Less was developed by the less project and is distributed under the Apache Software License 2.0.

Less maintains backward compatibility with CSS, meaning any valid CSS is also valid Less code. The language adds conveniences like the ability to nest selectors to mirror HTML structure, define reusable mixins, use variables for repeated values, and perform calculations. Because Less syntax closely resembles CSS, developers can adopt it without a steep learning curve. The tool is written in JavaScript and works across different platforms.