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CSS variables

Learn about the experimental API for using CSS variables with Material UI components.

CSS variables provide significant improvements in developer experience related to theming and customization. With these variables, you can inject a theme into your app's stylesheet at build time to apply the user's selected settings before the whole app is rendered.

This solves the problem of dark-mode SSR flickering; lets you provide your users with multiple themes beyond light and dark; and offers a better debugging experience overall, among other benefits.

Previously, these CSS variables were only available as an experimental API in the MUI System package. Now they are ready for experimental use with Material UI components.

Introduction

The CSS variables API relies on a new experimental provider for the theme called Experimental_CssVarsProvider to inject styles into Material UI components. In addition to providing the theme in the inner React context, this new provider also generates CSS variables out of all tokens in the theme that are not functions, and makes them available in the context as well.

All of these variables are accessible in an object in the theme called vars. The structure of this object is nearly identical to the theme structure, the only difference is that the values represent CSS variables.

Usage

Experimental_CssVarsProvider is a new experimental provider that attaches all generated CSS variables to the theme and puts them in React's context. Children elements under this provider will also be able to read the CSS variables from the theme.vars.

import { Experimental_CssVarsProvider as CssVarsProvider } from '@mui/material/styles';

function App() {
  return <CssVarsProvider>...</CssVarsProvider>;
}

If you use TypeScript, check out the theme types setup.

Customizing components

Because the CSS variables API is an experimental feature, it is currently only supported by the Button component. To customize it using CSS variables, you'll need to wrap your application with Experimental_CssVarsProvider.

Play around with the demo below!

If you are using TypeScript you should use module augmentation to update the Theme structure:

import { Theme as MuiTheme } from '@mui/material/styles';

declare module '@mui/material/styles' {
  interface Theme {
    vars: Omit<
      MuiTheme,
      'typography' | 'mixins' | 'breakpoints' | 'direction' | 'transitions'
    >;
  }
}

Customizing the theme

If you want, for example, to override Material UI's default color schemes, you can use the experimental_extendTheme utility.

const theme = experimental_extendTheme({
  colorSchemes: {
    light: {
      palette: {
        primary: teal,
        secondary: deepOrange,
      },
    },
    dark: {
      palette: {
        primary: cyan,
        secondary: orange,
      },
    },
  },
});

If you are using ThemeProvider, you can replace it with the new experimental provider.

-import { ThemeProvider, createTheme } from '@mui/material/styles';
+import { Experimental_CssVarsProvider as CssVarsProvider } from '@mui/material/styles';

 function App() {
   return (
-    <ThemeProvider theme={createTheme()}>
-      ...
-    </ThemeProvider>
+    <CssVarsProvider>
+      ...
+    </CssVarsProvider>
   )
 }

Toggle between light and dark mode

Experimental_CssVarsProvider provides light and dark mode by default. It stores the user's selected mode and syncs it with the browser's local storage internally. You can read and update the mode via the useColorScheme API.

import {
  Experimental_CssVarsProvider as CssVarsProvider,
  useColorScheme,
} from '@mui/material/styles';

const ModeSwitcher = () => {
  const { mode, setMode } = useColorScheme();
  const [mounted, setMounted] = React.useState(false);

  React.useEffect(() => {
    setMounted(true);
  }, []);

  if (!mounted) {
    // for server-side rendering
    // Read more on https://github.com/pacocoursey/next-themes#avoid-hydration-mismatch
    return null;
  }

  return (
    <Button
      variant="outlined"
      onClick={() => {
        if (mode === 'light') {
          setMode('dark');
        } else {
          setMode('light');
        }
      }}
    >
      {mode === 'light' ? 'Dark' : 'Light'}
    </Button>
  );
};

function App() {
  return (
    <CssVarsProvider>
      <ModeSwitcher />
    </CssVarsProvider>
  );
}

Server-side rendering

To prevent the dark-mode SSR flickering during the hydration phase, place getInitColorSchemeScript() before the <Main /> tag.

Next.js

To use the API with a Next.js project, add the following code to the custom pages/_document.js file:

import Document, { Html, Head, Main, NextScript } from 'next/document';
import { getInitColorSchemeScript } from '@mui/material/styles';

export default class MyDocument extends Document {
  render() {
    return (
      <Html>
        <Head>...</Head>
        <body>
          {getInitColorSchemeScript()}
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}

Gatsby

To use the API with a Gatsby project, add the following code to the custom gatsby-ssr.js file:

import React from 'react';
import { getInitColorSchemeScript } from '@mui/material/styles';

export function onRenderBody({ setPreBodyComponents }) {
  setPreBodyComponents([
    <React.Fragment key="mui-init-color-scheme-script">
      {getInitColorSchemeScript()}
    </React.Fragment>,
  ]);
}

TypeScript

You need to import the theme augmentation to include theme.vars and other utilities related to CSS variables to the theme:

// this can be the root file of you application
import type {} from '@mui/material/themeCssVarsAugmentation';

Then, you will be able to access theme.vars in any of the styling APIs, for example the styled:

import { styled } from '@mui/material/styles';

const StyledComponent = styled('button')(({ theme }) => ({
  // typed-safe
  color: theme.vars.palette.primary.main,
}));

API

<CssVarsProvider> props

  • defaultMode?: 'light' | 'dark' | 'system' - Application's default mode (light by default)
  • disableTransitionOnChange : boolean - Disable CSS transitions when switching between modes
  • enableColorScheme: boolean - Indicate to the browser which color scheme is used (light or dark) for rendering built-in UI
  • prefix: string - CSS variable prefix
  • theme: ThemeInput - the theme provided to React's context
  • modeStorageKey?: string - localStorage key used to store application mode
  • attribute?: string - DOM attribute for applying color scheme

useColorScheme: () => ColorSchemeContextValue

  • mode: string - The user's selected mode
  • setMode: mode => {…} - Function for setting the mode. The mode is saved to internal state and local storage; if mode is null, it will be reset to the default mode

getInitColorSchemeScript: (options) => React.ReactElement

options

  • defaultMode?: 'light' | 'dark' | 'system': - Application's default mode before React renders the tree (light by default)
  • modeStorageKey?: string: - localStorage key used to store application mode
  • attribute?: string - DOM attribute for applying color scheme