Autoprefixer is a tool to parse CSS and add vendor prefixes to CSS rules using values from the Can I Use. This gem provides Ruby and Ruby on Rails integration with this JavaScript tool.

Sponsored by Evil Martians.

Add the autoprefixer-rails gem to your Gemfile:

gem "autoprefixer-rails"

Clear your cache

  rake tmp:clear

Write your CSS (Sass, Stylus, LESS) rules without vendor prefixes and Autoprefixer will apply prefixes for you. For example in app/assets/stylesheet/foobar.sass:

:fullscreen a
  transition: transform 1s

Autoprefixer uses Can I Use database with browser statistics and properties support to add vendor prefixes automatically using the Asset Pipeline:

:-webkit-full-screen a {
    -webkit-transition: -webkit-transform 1s;
            transition: transform 1s
}
:-moz-full-screen a {
    transition: transform 1s
}
:-ms-fullscreen a {
    transition: transform 1s
}
:fullscreen a {
    -webkit-transition: -webkit-transform 1s;
            transition: transform 1s
}

If you need to specify browsers for your Rails project, you can save them to config/autoprefixer.yml. See browser section in Autoprefixer docs.

browsers:
  - "last 1 version"
  - "> 1%"
  - "Explorer 10"

You can get what properties will be changed using a Rake task:

rake autoprefixer:info

By default, Autoprefixer uses > 1%, last 2 versions, Firefox ESR, Opera 12.1:

• Latest Firefox ESR is a 24 version.
• Opera 12.1 will be in list until Opera supports non-Blink 12.x branch.

If you use Sinatra or other non-Rails frameworks with Sprockets, just connect your Sprockets environment with Autoprefixer and write CSS in the usual way:

assets = Sprockets::Environment.new do |env|
  # Your assets settings
end

require "autoprefixer-rails"
AutoprefixerRails.install(assets)

If you need to call Autoprefixer from plain Ruby code, it’s very easy:

require "autoprefixer-rails"
prefixed = AutoprefixerRails.process(css, from: 'main.css').css

You can specify browsers by browsers option:

AutoprefixerRails.process(css, from: 'a.css', browsers: ['> 1%', 'ie 10']).css

By default, Autoprefixer will change CSS indentation to create nice visual cascade of prefixes.

a {
  -webkit-box-sizing: border-box;
     -moz-box-sizing: border-box;
          box-sizing: border-box
}

You can disable it by cascade: false in config/autoprefixer.yml or in process() options.

If you have legacy code with non-valid CSS hacks, you can enable Safe Mode and Autoprefixer will try to fix broken CSS.

Add safe: on to config/autoprefixer.yml or use safe: true option in process method.

Autoprefixer will generate source map, if you set map option to true in process method.

You must set input and output CSS files paths (by from and to options) to generate correct map.

result = AutoprefixerRails.process(css,
    map:   true,
    from: 'main.css',
    to:   'main.out.css')

result.css #=> Prefixed CSS
result.map #=> Source map content

Autoprefixer can also modify previous source map (for example, from Sass compilation). Just set original source map content (as string) to map option:

result = AutoprefixerRails.process(css, {
    map:   File.read('main.sass.css.map'),
    from: 'main.sass.css',
    to:   'main.min.css')

result.map #=> Source map from main.sass to main.min.css

See all options in PostCSS docs. AutoprefixerRails will convert Ruby style to JS style, so you can use map: { sources_content: true } instead of camelcase sourcesContent.