Next.js has built-in support for integrating with Sass after the package is installed using both the .scss and .sass extensions. You can use component-level Sass via CSS Modules and the .module.scssor .module.sass extension.

First, install sass:

npm install --save-dev sass

Good to know:

Sass supports two different syntaxes, each with their own extension.
The .scss extension requires you use the SCSS syntax,
while the .sass extension requires you use the Indented Syntax ("Sass").

If you're not sure which to choose, start with the .scss extension which is a superset of CSS, and doesn't require you learn the
Indented Syntax ("Sass").

Customizing Sass Options

If you want to configure your Sass options, use sassOptions in next.config.

import type { NextConfig } from 'next'

const nextConfig: NextConfig = {
  sassOptions: {
    additionalData: `$var: red;`,
  },
}

export default nextConfig

/** @type {import('next').NextConfig} */

const nextConfig = {
  sassOptions: {
    additionalData: `$var: red;`,
  },
}

module.exports = nextConfig

Implementation

You can use the implementation property to specify the Sass implementation to use. By default, Next.js uses the sass package.

import type { NextConfig } from 'next'

const nextConfig: NextConfig = {
  sassOptions: {
    implementation: 'sass-embedded',
  },
}

export default nextConfig

/** @type {import('next').NextConfig} */

const nextConfig = {
  sassOptions: {
    implementation: 'sass-embedded',
  },
}

module.exports = nextConfig

Sass Variables

Next.js supports Sass variables exported from CSS Module files.

For example, using the exported primaryColor Sass variable:

$primary-color: #64ff00;

:export {
  primaryColor: $primary-color;
}

// maps to root `/` URL

import variables from './variables.module.scss'

export default function Page() {
  return <h1 style={{ color: variables.primaryColor }}>Hello, Next.js!</h1>
}

import variables from '../styles/variables.module.scss'

export default function MyApp({ Component, pageProps }) {
  return (
    <Layout color={variables.primaryColor}>
      <Component {...pageProps} />
    </Layout>
  )
}