Import .css files in your Next.js project with PostCSS.

npm install --save next-postcss

or

yarn add next-postcss

The stylesheet is compiled to .next/static/css. Next.js will automatically add the css file to the HTML. In production a chunk hash is added so that styles are updated when a new version of the stylesheet is deployed.

Create a next.config.js in the root of your project (next to pages/ and package.json)

// next.config.js
const withCSS = require('next-postcss');
module.exports = withCSS({
  /* config options here */
});

Create a CSS file style.css

.example {
  font-size: 50px;
}

Create a page file pages/index.js

import '../style.css';

export default () => <div className="example">Hello World!</div>;

Note: CSS files can not be imported into your _document.js. You can use the _app.js instead or any other page.

// next.config.js
const withCSS = require('next-postcss');
module.exports = withCSS({
  cssModules: true,
});

Create a CSS file style.css

.example {
  font-size: 50px;
}

Create a page file pages/index.js

import css from '../style.css';

export default () => <div className={css.example}>Hello World!</div>;

You can also pass a list of options to the css-loader by passing an object called cssLoaderOptions.

For instance, to enable locally scoped CSS modules, you can write:

// next.config.js
const withCSS = require('next-postcss');
module.exports = withCSS({
  cssModules: true,
  cssLoaderOptions: {
    importLoaders: 1,
    localIdentName: '[local]___[hash:base64:5]',
  },
});

Create a CSS file styles.css

.example {
  font-size: 50px;
}

Create a page file pages/index.js that imports your stylesheet and uses the hashed class name from the stylesheet

import css from '../style.css';

const Component = props => {
  return <div className={css.example}>...</div>;
};

export default Component;

Your exported HTML will then reflect locally scoped CSS class names.

For a list of supported options, refer to the webpack css-loader README.

Create a next.config.js in your project

// next.config.js
const withCSS = require('next-postcss');
module.exports = withCSS({
  /* config options here */
});

Create a postcss.config.js or .postcssrc

module.exports = {
  plugins: {
    // Illustrational
    'postcss-css-variables': {},
  },
};

Create a CSS file style.css the CSS here is using the css-variables postcss plugin.

:root {
  --some-color: red;
}

.example {
  /* red */
  color: var(--some-color);
}

When postcss.config.js or .postcss are not found postcss-loader will not be added and will not cause overhead.

You can also pass a list of options to the postcss-loader by passing an object called postcssLoaderOptions.

For example, to pass theme env variables to postcss-loader, you can write:

// next.config.js
const withCSS = require('next-postcss');
module.exports = withCSS({
  postcssLoaderOptions: {
    parser: true,
    postcssOptions: {
      ctx: {
        theme: JSON.stringify(process.env.REACT_APP_THEME),
      },
    },
  },
});

Optionally you can add your custom Next.js configuration as parameter

// next.config.js
const withCSS = require('next-postcss');
module.exports = withCSS({
  webpack(config, options) {
    return config;
  },
});