Bootstrap is an open source toolkit for developing with HTML, CSS, and JS. Quickly prototype your ideas or build your entire app with our Sass variables and mixins, responsive grid system, extensive prebuilt components, and powerful plugins built on jQuery.
Build responsive, mobile-first projects on the web with the world's most popular front-end component library.
Sass is a meta-language on top of CSS that's used to describe the style of a document cleanly and structurally, with more power than flat CSS allows. ... More specifically, Sass is an extension of CSS3, and its SCSS (“Sassy CSS”) syntaxis a superset of CSS3.
Less is a CSS pre-processor, meaning that it extends the CSS language, adding features that allow variables, mixins, functions and many other techniques that allow you to make CSS that is more maintainable, themeable and extendable. ... The quickest place for first experiments with Less is our online editor.