It's CSS, with just a little more. The dynamic stylesheet language.

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.

Less.js @ GitHub.

A collection of pure CSS3 lightweight animations that can be applied to links, sections, buttons and much more. Available in SCSS, CSS and LESS.
Annimay @ GitHub

A collection of CSS3 powered hover effects to be applied to links, buttons, logos, SVG, featured images and so on. Easily apply to your own elements, modify or just use for inspiration. Available in CSS, SASS, and LESS.

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Convert css to less

The first thing to point out is that this isn't a kitchen sink project like HTML5 Boilerplate. In fact it's not a template or widget library at all. FE-Patterns is a web stack pattern reference. These patterns are for you to tinker around with. Create your own HTML and use LESS files to style it.