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Importing CSS in React Server Components

tip

Hydrogen 2.0 is out now. These archival Hydrogen 1.0 docs are provided only to assist developers during their upgrade process. Please migrate to Hydrogen 2.0 as soon as possible.

Hydrogen collects styles for each CSS file imported in your client and server components.

Modify modes for CSS support​

You can modify the following modes for CSS support by passing experimental.css option to the Hydrogen plugin in vite.config.js:

// vite.config.js

export default defineConfig({
  plugins: [hydrogen({experimental: {css: 'global'}})]
})
  • modules-only: Enables limited support for CSS Modules only. This is the current default mode.
  • global: Enables full support for vanilla CSS and CSS Modules. global also enables a way to integrate with tools that provide CSS-in-JS at build time. This is the recommended mode.

Note: CSS code split for different routes is not currently supported.

Import Vanilla (pure) CSS and extensions​

Vanilla CSS and language extensions such as Sass, Less, and Stylus are supported under the experimental.css: 'global' feature.

Once enabled, you can import your stylesheets directly in your server components:

// App.server.jsx

import './my-style.css';
import './another-style.sass';

function App() {
  return <div>...</div>
}

Import CSS Modules​

Hydrogen collects styles for each CSS Module in your components. CSS Modules can be imported in both client and server components.

// src/components/Hello.server.jsx

import {red} from './styles.module.css';

export default function MyComponent() {
  return (
    <div className={red}>
      <p>Hello</p>
    </div>
  );
}

When the CSS mode is modules-only, styles are inlined in a <style> tag before your component. This tag is only added automatically for the default export in the file. Consider using the global CSS mode to support named exports and reduce code duplication.

CSS-in-JS libraries​

Hydrogen supports CSS-in-JS libraries that emit .css files at build time using third-party Vite plugins. Please reach out to the library maintainers to ask for React Server Components support, and feel free to tag the Hydrogen team (@shopify/hydrogen).

However, CSS-in-JS libraries that collect styles at runtime aren't currently supported due to limitation integrating these libraries with React Server Components.

Next steps​