CSS Loader

npm install --save-dev css-loader

The css-loader interprets @import and url() like import/require() and will resolve them.

Good loaders for requiring your assets are the file-loader and the url-loader which you should specify in your config (see below).

file.js

import css from 'file.css';

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ 'style-loader', 'css-loader' ]
      }
    ]
  }
}

You can also use the css-loader results directly as string, such as in Angular's component style.

webpack.config.js

{
   test: /\.css$/,
   use: [
     'to-string-loader',
     'css-loader'
   ]
}

or

const css = require('./test.css').toString();

console.log(css); // {String}

If there are SourceMaps, they will also be included in the result string.

If, for one reason or another, you need to extract CSS as a plain string resource (i.e. not wrapped in a JS module) you might want to check out the extract-loader. It's useful when you, for instance, need to post process the CSS as a string.

webpack.config.js

{
   test: /\.css$/,
   use: [
     'handlebars-loader', // handlebars loader expects raw resource string
     'extract-loader',
     'css-loader'
   ]
}

For URLs that start with a /, the default behavior is to not translate them.

url(/image.png) => url(/image.png)

If a root query parameter is set, however, it will be prepended to the URL and then translated.

webpack.config.js

{
  loader: 'css-loader',
  options: { root: '.' }
}

url(/image.png) => require('./image.png')

Using 'Root-relative' urls is not recommended. You should only use it for legacy CSS files.

To disable url() resolving by css-loader set the option to false.

To be compatible with existing css files (if not in CSS Module mode).

url(image.png) => require('./image.png')
url(~module/image.png) => require('module/image.png')

Rewrite your urls with alias, this is useful when it's hard to change url paths of your input files, for example, when you're using some css / sass files in another package (bootstrap, ratchet, font-awesome, etc.).

css-loader's alias follows the same syntax as webpack's resolve.alias, you can see the details at the resolve docs

file.scss

@charset "UTF-8";
@import "bootstrap";

webpack.config.js

{
  test: /\.scss$/,
  use: [
    {
      loader: "style-loader"
    },
    {
      loader: "css-loader",
      options: {
        alias: {
          "../fonts/bootstrap": "bootstrap-sass/assets/fonts/bootstrap"
        }
      }
    },
    {
      loader: "sass-loader",
      options: {
        includePaths: [
          path.resolve("./node_modules/bootstrap-sass/assets/stylesheets")
        ]
      }
    }
  ]
}

Check out this working bootstrap example.

To disable @import resolving by css-loader set the option to false

@import url('https://fonts.googleapis.com/css?family=Roboto');

⚠️ Use with caution, since this disables resolving for all @imports, including css modules composes: xxx from 'path/to/file.css' feature.

The query parameter modules enables the CSS Modules spec.

This enables local scoped CSS by default. (You can switch it off with :global(...) or :global for selectors and/or rules.).

By default CSS exports all classnames into a global selector scope. Styles can be locally scoped to avoid globally scoping styles.

The syntax :local(.className) can be used to declare className in the local scope. The local identifiers are exported by the module.

With :local (without brackets) local mode can be switched on for this selector. :global(.className) can be used to declare an explicit global selector. With :global (without brackets) global mode can be switched on for this selector.

The loader replaces local selectors with unique identifiers. The choosen unique identifiers are exported by the module.

:local(.className) { background: red; }
:local .className { color: green; }
:local(.className .subClass) { color: green; }
:local .className .subClass :global(.global-class-name) { color: blue; }

._23_aKvs-b8bW2Vg3fwHozO { background: red; }
._23_aKvs-b8bW2Vg3fwHozO { color: green; }
._23_aKvs-b8bW2Vg3fwHozO ._13LGdX8RMStbBE9w-t0gZ1 { color: green; }
._23_aKvs-b8bW2Vg3fwHozO ._13LGdX8RMStbBE9w-t0gZ1 .global-class-name { color: blue; }

ℹ️ Identifiers are exported

exports.locals = {
  className: '_23_aKvs-b8bW2Vg3fwHozO',
  subClass: '_13LGdX8RMStbBE9w-t0gZ1'
}

CamelCase is recommended for local selectors. They are easier to use in the within the imported JS module.

url() URLs in block scoped (:local .abc) rules behave like requests in modules.

file.png => ./file.png
~module/file.png => module/file.png

You can use :local(#someId), but this is not recommended. Use classes instead of ids. You can configure the generated ident with the localIdentName query parameter (default [hash:base64]).

webpack.config.js

{
 test: /\.css$/,
 use: [
   {
     loader: 'css-loader',
     options: {
       modules: true,
       localIdentName: '[path][name]__[local]--[hash:base64:5]'
     }
   }
 ]
}

You can also specify the absolute path to your custom getLocalIdent function to generate classname based on a different schema. This requires webpack >= 2.2.1 (it supports functions in the options object).

webpack.config.js

{
  loader: 'css-loader',
  options: {
    modules: true,
    localIdentName: '[path][name]__[local]--[hash:base64:5]',
    getLocalIdent: (context, localIdentName, localName, options) => {
      return 'whatever_random_class_name'
    }
  }
}

ℹ️ For prerendering with extract-text-webpack-plugin you should use css-loader/locals instead of style-loader!css-loader in the prerendering bundle. It doesn't embed CSS but only exports the identifier mappings.

When declaring a local classname you can compose a local class from another local classname.

:local(.className) {
  background: red;
  color: yellow;
}

:local(.subClass) {
  composes: className;
  background: blue;
}

This doesn't result in any change to the CSS itself but exports multiple classnames.

exports.locals = {
  className: '_23_aKvs-b8bW2Vg3fwHozO',
  subClass: '_13LGdX8RMStbBE9w-t0gZ1 _23_aKvs-b8bW2Vg3fwHozO'
}

._23_aKvs-b8bW2Vg3fwHozO {
  background: red;
  color: yellow;
}

._13LGdX8RMStbBE9w-t0gZ1 {
  background: blue;
}

To import a local classname from another module.

:local(.continueButton) {
  composes: button from 'library/button.css';
  background: red;
}

:local(.nameEdit) {
  composes: edit highlight from './edit.css';
  background: red;
}

To import from multiple modules use multiple composes: rules.

:local(.className) {
  composes: edit hightlight from './edit.css';
  composes: button from 'module/button.css';
  composes: classFromThisModule;
  background: red;
}

By default the css-loader minimizes the css if specified by the module system.

In some cases the minification is destructive to the css, so you can provide your own options to the cssnano-based minifier if needed. See cssnano's documentation for more information on the available options.

You can also disable or enforce minification with the minimize query parameter.

webpack.config.js

{
  loader: 'css-loader',
  options: {
    minimize: true || {/* CSSNano Options */}
  }
}

To include source maps set the sourceMap option.

I. e. the extract-text-webpack-plugin can handle them.

They are not enabled by default because they expose a runtime overhead and increase in bundle size (JS source maps do not). In addition to that relative paths are buggy and you need to use an absolute public path which include the server URL.

webpack.config.js

{
  loader: 'css-loader',
  options: {
    sourceMap: true
  }
}

By default, the exported JSON keys mirror the class names. If you want to camelize class names (useful in JS), pass the query parameter camelCase to css-loader.

file.css

.class-name {}

file.js

import { className } from 'file.css';

webpack.config.js

{
  loader: 'css-loader',
  options: {
    camelCase: true
  }
}

The query parameter importLoaders allows to configure how many loaders before css-loader should be applied to @imported resources.

webpack.config.js

{
  test: /\.css$/,
  use: [
    'style-loader',
    {
      loader: 'css-loader',
      options: {
        importLoaders: 2 // 0 => no loaders (default); 1 => postcss-loader; 2 => postcss-loader, sass-loader
      }
    },
    'postcss-loader',
    'sass-loader'
  ]
}

This may change in the future, when the module system (i. e. webpack) supports loader matching by origin.

The following webpack.config.js can load CSS files, embed small PNG/JPG/GIF/SVG images as well as fonts as Data URLs and copy larger files to the output directory.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ 'style-loader', 'css-loader' ]
      },
      {
        test: /\.(png|jpg|gif|svg|eot|ttf|woff|woff2)$/,
        loader: 'url-loader',
        options: {
          limit: 10000
        }
      }
    ]
  }
}

For production builds it's recommended to extract the CSS from your bundle being able to use parallel loading of CSS/JS resources later on. This can be achieved by using the extract-text-webpack-plugin to extract the CSS when running in production mode.

webpack.config.js

const env = process.env.NODE_ENV

const ExtractTextPlugin = require('extract-text-webpack-plugin')

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: env === 'production'
          ? ExtractTextPlugin.extract({
              fallback: 'style-loader',
              use: [ 'css-loader' ]
          })
          : [ 'style-loader', 'css-loader' ]
      },
    ]
  },
  plugins: env === 'production'
    ? [
        new ExtractTextPlugin({
          filename: '[name].css'
        })
      ]
    : []
}

To create a webpack build of isomorphic/universal web application that pre-renders pages on the server side you might need to bundle CSS dependencies, such as bootstrap.min.css, installed from node_modules.

There are several caveats in loading CSS in server-side environment:

1. style-loader can't be used in server-side node.js, because it refers to window global when trying to inline your css into the javascript bundle. You need to use extract-text-webpack-plugin with css-loader to extract styles into a separate file.
2. target: node setting and webpack-node-externals package should be used to keep standard node.js modules and javascript dependencies from node_modules outside of the bundle.
3. with default webpack-node-externals setup, CSS that resides in node_modules will also be excluded from the bundle. Imports of CSS files in sources will be replaced with require('bootstrap.min.css') statements in the bundle as if they were javascript, which results in SyntaxError in runtime. Thus non-javascript dependencies in node_modules need to be whitelisted from externals.

webpack.config.js

const ExtractTextPlugin = require('extract-text-webpack-plugin');
const nodeExternals = require('webpack-node-externals');

module.exports = {
  target: 'node', // don't bundle standard node.js modules such as http or path
  externals: [nodeExternals({ // don't bundle dependencies from node_modules folder, except by non-javascript files
    whitelist: [ // non-javascript files in node_modules should go to the bundle and be processed by ExtractTextPlugin
      /\.(?!(?:jsx?|json)$).{1,5}$/i,
    ],
  })],
  plugins: [
    new ExtractTextPlugin('server.css') // extract css files into server.css bundle
  ],
  ...
  module: {
    rules: [
      ...
      {
        test: /\.css$/,
        use: ExtractTextPlugin.extract({
          use: [
            { loader: 'css-loader', options: {sourceMap: true} }
          ]
        })
      },
      ...
    ]
  }
};

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