LESS (http://lesscss.org/) is a JavaScript-based CSS preprocessor developed by Alexis Sellier (http://cloudhead.io/), also known as CloudHead. As mentioned, Bootstrap uses LESS to compose its component styles—though it only recently released the Sass version officially. As mentioned, we will follow Bootstrap to use LESS to compose our own style rules and manage style sheets.

In a nutshell, LESS extends CSS by bringing some programming features, such as variable, function, and operation. CSS is a straightforward language and fundamentally very easy to learn. However, maintaining static CSS is practically exhaustive, particularly when we have to deal with a thousand lines of style rules and multiple style sheets. The capabilities that LESS offers, such as variable, mixins, function, and operation (which we are going to take a look at shortly) will allow us to develop style rules that will be easier to maintain and organize.