How to use CSS in your application

Next.js provides several ways to use CSS in your application, including:

• CSS Modules
• Global CSS
• External Stylesheets
• Tailwind CSS
• Sass
• CSS-in-JS

CSS Modules

CSS Modules locally scope CSS by generating unique class names. This allows you to use the same class in different files without worrying about naming collisions.

To start using CSS Modules, create a new file with the extension .module.css and import it into any component inside the pages directory:

.blog {
  padding: 24px;
}

import styles from './blog.module.css'
 
export default function Page() {
  return <main className={styles.blog}></main>
}

Global CSS

You can use global CSS to apply styles across your application.

Import the stylesheet in the pages/_app.js file to apply the styles to every route in your application:

import '@/styles/global.css'
 
export default function MyApp({ Component, pageProps }) {
  return <Component {...pageProps} />
}

Due to the global nature of stylesheets, and to avoid conflicts, you should import them inside pages/_app.js.

External stylesheets

Next.js allows you to import CSS files from a JavaScript file. This is possible because Next.js extends the concept of import beyond JavaScript.

Import styles from node_modules

Since Next.js 9.5.4, importing a CSS file from node_modules is permitted anywhere in your application.

For global stylesheets, like bootstrap or nprogress, you should import the file inside pages/_app.js. For example:

import 'bootstrap/dist/css/bootstrap.css'
 
export default function MyApp({ Component, pageProps }) {
  return <Component {...pageProps} />
}

To import CSS required by a third-party component, you can do so in your component. For example:

import { useState } from 'react'
import { Dialog } from '@reach/dialog'
import VisuallyHidden from '@reach/visually-hidden'
import '@reach/dialog/styles.css'
 
function ExampleDialog(props) {
  const [showDialog, setShowDialog] = useState(false)
  const open = () => setShowDialog(true)
  const close = () => setShowDialog(false)
 
  return (
    <div>
      <button onClick={open}>Open Dialog</button>
      <Dialog isOpen={showDialog} onDismiss={close}>
        <button className="close-button" onClick={close}>
          <VisuallyHidden>Close</VisuallyHidden>
          <span aria-hidden>×</span>
        </button>
        <p>Hello there. I am a dialog</p>
      </Dialog>
    </div>
  )
}

Ordering and Merging

Next.js optimizes CSS during production builds by automatically chunking (merging) stylesheets. The order of your CSS depends on the order you import styles in your code.

For example, base-button.module.css will be ordered before page.module.css since <BaseButton> is imported before page.module.css:

import { BaseButton } from './base-button'
import styles from './page.module.css'
 
export default function Page() {
  return <BaseButton className={styles.primary} />
}

import styles from './base-button.module.css'
 
export function BaseButton() {
  return <button className={styles.primary} />
}

Recommendations

To keep CSS ordering predictable:

• Try to contain CSS imports to a single JavaScript or TypeScript entry file
• Import global styles and Tailwind stylesheets in the root of your application.
• Use CSS Modules instead of global styles for nested components.
• Use a consistent naming convention for your CSS modules. For example, using <name>.module.css over <name>.tsx.
• Extract shared styles into shared components to avoid duplicate imports.
• Turn off linters or formatters that auto-sort imports like ESLint’s sort-imports.
• You can use the cssChunking option in next.config.js to control how CSS is chunked.

Development vs Production

• In development (next dev), CSS updates apply instantly with Fast Refresh.
• In production (next build), all CSS files are automatically concatenated into many minified and code-split .css files, ensuring the minimal amount of CSS is loaded for a route.
• CSS still loads with JavaScript disabled in production, but JavaScript is required in development for Fast Refresh.
• CSS ordering can behave differently in development, always ensure to check the build (next build) to verify the final CSS order.