Heads up! This page is still under construction and is missing plenty of documentation. Hang tight!

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.

Why LESS?

Bootstrap is made with LESS at it's core, a dynamic stylesheet language created by 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

LESS CSS

Visit the official website at http://lesscss.org to learn more.

Variables

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.

Mixins

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.

Operations

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

Hyperlinks

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

Grayscale colors

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

Accent colors

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

Grid system

Variable Value
@gridColumns 12
@gridColumnWidth 60px
@gridGutterWidth 20px
@siteWidth (@gridColumns * @gridColumnWidth) + (@gridGutterWidth * (@gridColumns - 1))

Typography

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

Components

Buttons

@primaryButtonColor @blue

Forms

@placeholderText @grayLight

Navbar

@navbarHeight 40px
@navbarBackground @grayDarker
@navbarBackgroundHighlight @grayDark

Form states and alerts

@warningText #f3edd2
@warningBackground #c09853
@warningBorder #f3edd2
@errorText #b94a48
@errorBackground #f2dede
@errorBorder #e9c7c7
@successText #468847
@successBackground #dff0d8
@successBorder #cfe8c4
@infoText #3a87ad
@infoBackground #d9edf7
@infoBorder #bfe1f2

Bootstrap was built with Preboot, an open-source pack of mixins and variables to be used in conjunction with Less, a CSS preprocessor for faster and easier web development.

Check out how we used Preboot in Bootstrap and how you can make use of it should you choose to run Less on your next project.

How to use it

Use this option to make full use of Bootstrap’s Less variables, mixins, and nesting in CSS via javascript in your browser.

<link rel="stylesheet/less" href="less/bootstrap.less" media="all" />
<script src="js/less-1.1.3.min.js"></script>

Not feeling the .js solution? Try the Less Mac app or use Node.js to compile when you deploy your code.

What’s included

Here are some of the highlights of what’s included in Twitter Bootstrap as part of Bootstrap. Head over to the Bootstrap website or Github project page to download and learn more.

Variables

Variables in Less are perfect for maintaining and updating your CSS headache free. When you want to change a color value or a frequently used value, update it in one spot and you’re set.

// Links
@linkColor:         #8b59c2;
@linkColorHover:    darken(@linkColor, 10);

// Grays
@black:             #000;
@grayDark:          lighten(@black, 25%);
@gray:              lighten(@black, 50%);
@grayLight:         lighten(@black, 70%);
@grayLighter:       lighten(@black, 90%);
@white:             #fff;

// Accent Colors
@blue:              #08b5fb;
@green:             #46a546;
@red:               #9d261d;
@yellow:            #ffc40d;
@orange:            #f89406;
@pink:              #c3325f;
@purple:            #7a43b6;

// Baseline grid
@basefont:          13px;
@baseline:          18px;

Commenting

Less also provides another style of commenting in addition to CSS’s normal /* ... */ syntax.

// This is a comment
/* This is also a comment */

Mixins up the wazoo

Mixins are basically includes or partials for CSS, allowing you to combine a block of code into one. They’re great for vendor prefixed properties like box-shadow, cross-browser gradients, font stacks, and more. Below is a sample of the mixins that are included with Bootstrap.

Font stacks

#font {
  .shorthand(@weight: normal, @size: 14px, @lineHeight: 20px) {
    font-size: @size;
    font-weight: @weight;
    line-height: @lineHeight;
  }
  .sans-serif(@weight: normal, @size: 14px, @lineHeight: 20px) {
    font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
    font-size: @size;
    font-weight: @weight;
    line-height: @lineHeight;
  }
  ...
}

Gradients

#gradient {
  ...
  .vertical (@startColor: #555, @endColor: #333) {
    background-color: @endColor;
    background-repeat: repeat-x;
    background-image: -khtml-gradient(linear, left top, left bottom, from(@startColor), to(@endColor)); // Konqueror
    background-image: -moz-linear-gradient(@startColor, @endColor); // FF 3.6+
    background-image: -ms-linear-gradient(@startColor, @endColor); // IE10
    background-image: -webkit-gradient(linear, left top, left bottom, color-stop(0%, @startColor), color-stop(100%, @endColor)); // Safari 4+, Chrome 2+
    background-image: -webkit-linear-gradient(@startColor, @endColor); // Safari 5.1+, Chrome 10+
    background-image: -o-linear-gradient(@startColor, @endColor); // Opera 11.10
    background-image: linear-gradient(@startColor, @endColor); // The standard
  }
  ...
}

Operations

Get fancy and perform some math to generate flexible and powerful mixins like the one below.

// Griditude
@gridColumns:       16;
@gridColumnWidth:   40px;
@gridGutterWidth:   20px;
@siteWidth:         (@gridColumns * @gridColumnWidth) + (@gridGutterWidth * (@gridColumns - 1));

// Make some columns
.columns(@columnSpan: 1) {
  width: (@gridColumnWidth * @columnSpan) + (@gridGutterWidth * (@columnSpan - 1));
}

Compiling Less

After modifying the .less files in /lib/, you'll need to recompile them in order to regenerate the bootstrap-*.*.*.css and bootstrap-*.*.*.min.css files. If you're submitting a pull request to GitHub, you must always recompile.

Ways to compile

Method Steps
Node with makefile

Install the LESS command line compiler with npm by running the following command:

$ npm install less

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).

Javascript

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.

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!

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.

Crunch Crunch is a great looking LESS editor and compiler built on Adobe Air.
CodeKit Created by the same guy as the unofficial Mac app, CodeKit is a Mac app that compiles LESS, SASS, Stylus, and CoffeeScript.
Simpless Mac, Linux, and PC app for drag and drop compiling of LESS files. Plus, the source code is on GitHub.