#CSS

Rspack has built-in support for CSS and provides several features to support CSS bundling.

#Enabling CSS support

You can choose from the following options:

#Built-in CSS support

Rspack supports the following four CSS Modules types which you can configure manually:

• css/auto: Automatically determines whether a file is a normal CSS file or CSS Modules based on the file extension. Files ending with *.module.css or *.modules.css are treated as CSS Modules.
• css: Used to handle normal CSS files without CSS Modules features.
• css/global: Used to handle CSS Modules in global scope mode.
• css/module: Used to handle CSS Modules.

The difference between css/auto, css/global, and css/module is how CSS Modules scope affects the generated CSS:

• css/auto chooses the behavior by filename. style.css is handled as plain CSS, while style.module.css and style.modules.css are handled like css/module.
• css/module enables CSS Modules with local scope by default. A selector like .button is renamed in the generated CSS. Use :global(.button) when you want a selector to stay global.
• css/global enables CSS Modules with global scope by default. A selector like .button stays global. Use :local(.button) when you want a selector to be renamed in the generated CSS.

For example:

.button {
  color: red;
}

:local(.title) {
  color: blue;
}

With type: 'css', the file is emitted as plain CSS without applying CSS Modules scope transforms.

With type: 'css/module', .button and .title are local selectors and are renamed in the generated CSS. Use :global(.button) if .button should stay global.

With type: 'css/global', .button stays global, while .title is renamed because it is wrapped in :local(...).

The generated CSS would look like this:

.button {
  color: red;
}

:local(.title) {
  color: blue;
}

._button_hash {
  color: red;
}

._title_hash {
  color: blue;
}

._button_hash {
  color: red;
}

._title_hash {
  color: blue;
}

.button {
  color: red;
}

._title_hash {
  color: blue;
}

To enable CSS support, add CSS rules to your configuration:

export default {
  module: {
    rules: [
      {
        test: /\.module\.css$/i,
        type: 'css/module',
      },
      {
        test: /\.global\.css$/i,
        type: 'css/global',
      },
      {
        test: /\.css$/i,
        type: 'css/auto',
      },
    ],
  },
};

You can also configure type: 'css/auto' to customize which files are treated as CSS files. For example, treat .less files as CSS files:

export default {
  module: {
    rules: [
      {
        test: /\.less$/,
        type: 'css/auto', // 👈
        use: ['less-loader'],
      },
    ],
  },
};

#Using CssExtractRspackPlugin

Rspack supports using css-loader and CssExtractRspackPlugin to generate standalone CSS files.

If you are migrating a webpack project that uses mini-css-extract-plugin, it is recommended to replace it with CssExtractRspackPlugin. Their functionality and options are basically the same.

• Install css-loader:

npm add css-loader -D

yarn add css-loader -D

pnpm add css-loader -D

bun add css-loader -D

deno add npm:css-loader -D

• Add configuration:

import { rspack } from '@rspack/core';

export default {
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: [rspack.CssExtractRspackPlugin.loader, 'css-loader'],
        type: 'javascript/auto',
      },
    ],
  },
  plugins: [new rspack.CssExtractRspackPlugin({})],
};

Refer to the migration guide to learn how to migrate from webpack.

#Using style-loader

Rspack supports using css-loader and style-loader to inject CSS via <style> tags. This method does not generate standalone CSS files but inline the CSS content into JS files.

• Install css-loader and style-loader:

npm add css-loader style-loader -D

yarn add css-loader style-loader -D

pnpm add css-loader style-loader -D

bun add css-loader style-loader -D

deno add npm:css-loader npm:style-loader -D

• Add configuration:

export default {
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: ['style-loader', 'css-loader'],
        type: 'javascript/auto',
      },
    ],
  },
};

#CSS Modules

CSS Modules is a way of organizing CSS files that localizes the scope of CSS by automatically generating unique identifiers for class names. This allows you to use the same class name in different files without worrying about collisions.

#Built-in support

If you enable Built-in CSS support, Rspack will treat files with a *.module.css extension as CSS Modules by default. You can import them into your JavaScript files, and then access each class defined in the CSS file as an export from the module.

.red {
  color: red;
}

You can use namespace import:

import * as styles from './index.module.css';
document.getElementById('element').className = styles.red;

You can also use named import:

import { red } from './index.module.css';
document.getElementById('element').className = red;

To enable default imports in Rspack, you need to set namedExports to false in your Rspack configuration file. This allows you, when using CSS Modules, to import the entire style module by default import, in addition to namespace imports and named imports:

export default {
  module: {
    parser: {
      'css/auto': {
        namedExports: false,
      },
    },
  },
};

Now you can use default import:

import styles from './index.module.css';
document.getElementById('element').className = styles.red;

#Using css-loader

If you do not enable Rspack's built-in CSS support, you can use css-loader to provide CSS Modules support.

Enable the modules option of css-loader:

export default {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        type: 'javascript/auto',
        options: {
          modules: true,
        },
      },
    ],
  },
};

For more usage, please refer to css-loader - modules.

#PostCSS

Rspack supports postcss-loader, which you can configure like this:

npm add postcss postcss-loader -D

yarn add postcss postcss-loader -D

pnpm add postcss postcss-loader -D

bun add postcss postcss-loader -D

deno add npm:postcss npm:postcss-loader -D

export default {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          {
            loader: 'postcss-loader',
            options: {
              postcssOptions: {
                // ...
              },
            },
          },
        ],
        // set to 'css/auto' if you want to support '*.module.css' as CSS Modules, otherwise set type to 'css'
        type: 'css/auto',
      },
    ],
  },
};

The above configuration will have all *.css files processed by postcss-loader. The output will be passed to Rspack for CSS post-processing.

#Sass

Rspack supports sass-loader, which you can configure like this:

npm add sass-embedded sass-loader -D

yarn add sass-embedded sass-loader -D

pnpm add sass-embedded sass-loader -D

bun add sass-embedded sass-loader -D

deno add npm:sass-embedded npm:sass-loader -D

export default {
  module: {
    rules: [
      {
        test: /\.(sass|scss)$/,
        use: [
          {
            loader: 'sass-loader',
            options: {
              // using `modern-compiler` and `sass-embedded` together significantly improve build performance,
              // requires `sass-loader >= 14.2.1`
              api: 'modern-compiler',
              implementation: require.resolve('sass-embedded'),
            },
          },
        ],
        // set to 'css/auto' if you want to support '*.module.(scss|sass)' as CSS Modules, otherwise set type to 'css'
        type: 'css/auto',
      },
    ],
  },
};

The above configuration runs all *.sass and *.scss files through the sass-loader and passes the resulting results to Rspack for CSS post-processing.

#Less

Rspack supports less-loader, which you can configure like this:

npm add less less-loader -D

yarn add less less-loader -D

pnpm add less less-loader -D

bun add less less-loader -D

deno add npm:less npm:less-loader -D

export default {
  module: {
    rules: [
      {
        test: /\.less$/,
        use: [
          {
            loader: 'less-loader',
            options: {
              // ...
            },
          },
        ],
        // set to 'css/auto' if you want to support '*.module.less' as CSS Modules, otherwise set type to 'css'
        type: 'css/auto',
      },
    ],
  },
};

The above configuration runs all *.less files through the less-loader and passes the generated results to Rspack for CSS post-processing.

#Tailwind CSS

Tailwind CSS is a CSS framework and design system based on utility class, which can quickly add common styles to components, and support flexible extension of theme styles.

Tailwind CSS documentation provides integration guides for Rspack, please refer to:

• Install Tailwind CSS v4 with Rspack
• Install Tailwind CSS v3 with Rspack