Less.js

Less (which stands for Leaner Style Sheets) is a backwards-compatible language extension for CSS. This is the official documentation for Less, the language and Less.js, the JavaScript tool that converts your Less styles to CSS styles. Because Less looks just like CSS, learning it is a breeze. Less only makes a few convenient additions to the CSS language, which is one of the reasons it can be learned so quickly. Less gives you the ability to use nesting instead of, or in combination with cascading. Arithmetical operations can operate on any number, color or variable. If it is possible, mathematical operations take units into account and convert numbers before adding, subtracting or comparing them. The result has leftmost explicitly stated unit type. If the conversion is impossible or not meaningful, units are ignored. With Less you can transform colors, manipulate strings and do maths.