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

$ npm install less

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

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