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App Router...StylingCSS Modules

CSS Modules and Global Styles

Next.js supports different types of stylesheets, including:

CSS Modules

Next.js has built-in support for CSS Modules using the .module.css extension.

CSS Modules locally scope CSS by automatically creating a unique class name. This allows you to use the same class name in different files without worrying about collisions. This behavior makes CSS Modules the ideal way to include component-level CSS.

Example

CSS Modules can be imported into any file inside the app directory:

app/dashboard/layout.tsx
import styles from './styles.module.css'
 
export default function DashboardLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return <section className={styles.dashboard}>{children}</section>
}
app/dashboard/styles.module.css
.dashboard {
  padding: 24px;
}

CSS Modules are only enabled for files with the .module.css and .module.sass extensions.

In production, all CSS Module files will be automatically concatenated into many minified and code-split .css files. These .css files represent hot execution paths in your application, ensuring the minimal amount of CSS is loaded for your application to paint.

Global Styles

Global styles can be imported into any layout, page, or component inside the app directory.

Good to know: This is different from the pages directory, where you can only import global styles inside the _app.js file.

For example, consider a stylesheet named app/global.css:

body {
  padding: 20px 20px 60px;
  max-width: 680px;
  margin: 0 auto;
}

Inside the root layout (app/layout.js), import the global.css stylesheet to apply the styles to every route in your application:

app/layout.tsx
// These styles apply to every route in the application
import './global.css'
 
export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <html lang="en">
      <body>{children}</body>
    </html>
  )
}

External Stylesheets

Stylesheets published by external packages can be imported anywhere in the app directory, including colocated components:

app/layout.tsx
import 'bootstrap/dist/css/bootstrap.css'
 
export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <html lang="en">
      <body className="container">{children}</body>
    </html>
  )
}

Good to know: External stylesheets must be directly imported from an npm package or downloaded and colocated with your codebase. You cannot use <link rel="stylesheet" />.

Ordering and Merging

Next.js optimizes CSS during production builds by automatically chunking (merging) stylesheets. The CSS order is determined by the order in which you import the stylesheets into your application code.

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

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

To maintain a predictable order, we recommend the following:

  • Only import a CSS file in a single JS/TS file.
    • If using global class names, import the global styles in the same file in the order you want them to be applied.
  • Prefer CSS Modules over global styles.
    • Use a consistent naming convention for your CSS modules. For example, using <name>.module.css over <name>.tsx.
  • Extract shared styles into a separate shared component.
  • If using Tailwind, import the stylesheet at the top of the file, preferably in the Root Layout.

Good to know: CSS ordering behaves differently in development mode, always ensure to check preview deployments to verify the final CSS order in your production build.

Additional Features

Next.js includes additional features to improve the authoring experience of adding styles:

  • When running locally with next dev, local stylesheets (either global or CSS modules) will take advantage of Fast Refresh to instantly reflect changes as edits are saved.
  • When building for production with next build, CSS files will be bundled into fewer minified .css files to reduce the number of network requests needed to retrieve styles.
  • If you disable JavaScript, styles will still be loaded in the production build (next start). However, JavaScript is still required for next dev to enable Fast Refresh.