Using LESS with Bootstrap

Customize and extend Bootstrap with LESS, a CSS preprocessor, to take advantage of the variables, mixins, and more used to build Bootstrap's CSS.


Bootstrap is made with LESS at its core, a dynamic stylesheet language created by our good friend, Alexis Sellier. It makes developing systems-based CSS faster, easier, and more fun.

What's included?

As an extension of CSS, LESS includes variables, mixins for reusable snippets of code, operations for simple math, nesting, and even color functions.

Learn more


Visit the official website at to learn more.


Managing colors and pixel values in CSS can be a bit of a pain, usually full of copy and paste. Not with LESS though—assign colors or pixel values as variables and change them once.


Those three border-radius declarations you need to make in regular ol' CSS? Now they're down to one line with the help of mixins, snippets of code you can reuse anywhere.


Make your grid, leading, and more super flexible by doing the math on the fly with operations. Multiply, divide, add, and subtract your way to CSS sanity.


@linkColor #08c Default link text color
@linkColorHover darken(@linkColor, 15%) Default link text hover color

Grid system

@gridColumns 12
@gridColumnWidth 60px
@gridGutterWidth 20px
@fluidGridColumnWidth 6.382978723%
@fluidGridGutterWidth 2.127659574%


@baseFontSize 13px
@baseFontFamily "Helvetica Neue", Helvetica, Arial, sans-serif
@baseLineHeight 18px

Grayscale colors

@black #000
@grayDarker #222
@grayDark #333
@gray #555
@grayLight #999
@grayLighter #eee
@white #fff

Accent colors

@blue #049cdb
@green #46a546
@red #9d261d
@yellow #ffc40d
@orange #f89406
@pink #c3325f
@purple #7a43b6



@primaryButtonBackground @linkColor


@placeholderText @grayLight


@navbarHeight 40px
@navbarBackground @grayDarker
@navbarBackgroundHighlight @grayDark
@navbarText @grayLight
@navbarLinkColor @grayLight
@navbarLinkColorHover @white

Form states and alerts

@warningText #c09853
@warningBackground #f3edd2
@errorText #b94a48
@errorBackground #f2dede
@successText #468847
@successBackground #dff0d8
@infoText #3a87ad
@infoBackground #d9edf7

About mixins

Basic mixins

A basic mixin is essentially an include or a partial for a snippet of CSS. They're written just like a CSS class and can be called anywhere.

.element {

Parametric mixins

A parametric mixin is just like a basic mixin, but it also accepts parameters (hence the name) with optional default values.

.element {

Easily add your own

Nearly all of Bootstrap's mixins are stored in mixins.less, a wonderful utility .less file that enables you to use a mixin in any of the .less files in the toolkit.

So, go ahead and use the existing ones or feel free to add your own as you need.

Included mixins


Mixin Parameters Usage
.clearfix() none Add to any parent to clear floats within
.tab-focus() none Apply the Webkit focus style and round Firefox outline
.center-block() none Auto center a block-level element using margin: auto
.ie7-inline-block() none Use in addition to regular display: inline-block to get IE7 support
.size() @height: 5px, @width: 5px Quickly set the height and width on one line
.square() @size: 5px Builds on .size() to set the width and height as same value
.opacity() @opacity: 100 Set, in whole numbers, the opacity percentage (e.g., "50" or "75")


Mixin Parameters Usage
.placeholder() @color: @placeholderText Set the placeholder text color for inputs


Mixin Parameters Usage
#font > #family > .serif() none Make an element use a serif font stack
#font > #family > .sans-serif() none Make an element use a sans-serif font stack
#font > #family > .monospace() none Make an element use a monospace font stack
#font > .shorthand() @size: @baseFontSize, @weight: normal, @lineHeight: @baseLineHeight Easily set font size, weight, and leading
#font > .serif() @size: @baseFontSize, @weight: normal, @lineHeight: @baseLineHeight Set font family to serif, and control size, weight, and leading
#font > .sans-serif() @size: @baseFontSize, @weight: normal, @lineHeight: @baseLineHeight Set font family to sans-serif, and control size, weight, and leading
#font > .monospace() @size: @baseFontSize, @weight: normal, @lineHeight: @baseLineHeight Set font family to monospace, and control size, weight, and leading

Grid system

Mixin Parameters Usage
.container-fixed() none Create a horizontally centered container for holding your content
#grid > .core() @gridColumnWidth, @gridGutterWidth Generate a pixel grid system (container, row, and columns) with n columns and x pixel wide gutter
#grid > .fluid() @fluidGridColumnWidth, @fluidGridGutterWidth Generate a precent grid system with n columns and x % wide gutter

CSS3 properties

Mixin Parameters Usage
.border-radius() @radius: 5px Round the corners of an element. Can be a single value or four space-separated values
.box-shadow() @shadow: 0 1px 3px rgba(0,0,0,.25) Add a drop shadow to an element
.transition() @transition Add CSS3 transition effect (e.g., all .2s linear)
.rotate() @degrees Rotate an element n degrees
.scale() @ratio Scale an element to n times its original size
.translate() @x: 0, @y: 0 Move an element on the x and y planes
.background-clip() @clip Crop the background of an element (useful for border-radius)
.background-size() @size Control the size of background images via CSS3
.box-sizing() @boxmodel Change the box model for an element (e.g., border-box for a full-width input)
.user-select() @select Control cursor selection of text on a page
.resizable() @direction: both Make any element resizable on the right and bottom
.content-columns() @columnCount, @columnGap: @gridColumnGutter Make the content of any element use CSS3 columns

Backgrounds and gradients

Mixin Parameters Usage
#translucent > .background() @color: @white, @alpha: 1 Give an element a translucent background color
#translucent > .border() @color: @white, @alpha: 1 Give an element a translucent border color
#gradient > .vertical() @startColor, @endColor Create a cross-browser vertical background gradient
#gradient > .horizontal() @startColor, @endColor Create a cross-browser horizontal background gradient
#gradient > .directional() @startColor, @endColor, @deg Create a cross-browser directional background gradient
#gradient > .vertical-three-colors() @startColor, @midColor, @colorStop, @endColor Create a cross-browser three-color background gradient
#gradient > .radial() @innerColor, @outerColor Create a cross-browser radial background gradient
#gradient > .striped() @color, @angle Create a cross-browser striped background gradient
#gradientBar() @primaryColor, @secondaryColor Used for buttons to assign a gradient and slightly darker border
Note: If you're submitting a pull request to GitHub with modified CSS, you must recompile the CSS via any of these methods.

Tools for compiling

Node with makefile

Install the LESS command line compiler and uglify-js globally with npm by running the following command:

$ npm install -g less uglify-js

Once installed just run make from the root of your bootstrap directory and you're all set.

Additionally, if you have watchr installed, you may run make watch to have bootstrap automatically rebuilt every time you edit a file in the bootstrap lib (this isn't required, just a convenience method).

Command line

Install the LESS command line tool via Node and run the following command:

$ lessc ./lib/bootstrap.less > bootstrap.css

Be sure to include --compress in that command if you're trying to save some bytes!


Download the latest Less.js and include the path to it (and Bootstrap) in the <head>.

<link rel="stylesheet/less" href="/path/to/bootstrap.less">
<script src="/path/to/less.js"></script>

To recompile the .less files, just save them and reload your page. Less.js compiles them and stores them in local storage.

Unofficial Mac app

The unofficial Mac app watches directories of .less files and compiles the code to local files after every save of a watched .less file.

If you like, you can toggle preferences in the app for automatic minifying and which directory the compiled files end up in.

More Mac apps


Crunch is a great looking LESS editor and compiler built on Adobe Air.


Created by the same guy as the unofficial Mac app, CodeKit is a Mac app that compiles LESS, SASS, Stylus, and CoffeeScript.


Mac, Linux, and PC app for drag and drop compiling of LESS files. Plus, the source code is on GitHub.