CSS theme variables - Customization

A guide for customizing CSS theme variables in Material UI.

Theming

experimental_extendTheme is an API that extends the default theme. It returns a theme that can only be used by the Experimental_CssVarsProvider.

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

const theme = extendTheme();
// ...custom theme

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

Color schemes

The major difference from the default approach is in palette customization. With the extendTheme API, you can specify the palette for all color schemes at once (light and dark are built in) under the colorSchemes node.

Here's an example of how to customize the primary palette:

import { pink } from '@mui/material/colors';

const theme = extendTheme({
  colorSchemes: {
    light: {
      palette: {
        primary: {
          main: pink[600],
        },
      },
    },
    dark: {
      palette: {
        primary: {
          main: pink[400],
        },
      },
    },
  },
});

Components

Component customization remains the same as the default approach. We recommend using the value from theme.vars.* whenever possible for a better debugging experience:

const theme = extendTheme({
  components: {
    MuiChip: {
      styleOverrides: {
        root: ({ theme, ownerState }) => ({
          ...(ownerState.variant === 'outlined' &&
            ownerState.color === 'primary' && {
              // this is the same as writing:
              // backgroundColor: 'var(--mui-palette-background-paper)',
              backgroundColor: theme.vars.palette.background.paper,
            }),
        }),
      },
    },
  },
});

Channel tokens

A channel token is a variable that consists of color space channels but without the alpha component. The value of a channel token is separated by a space, e.g. 12 223 31, which can be combined with the color functions to create a translucent color.

The extendTheme() automatically generates channel tokens that are likely to be used frequently from the theme palette. Those colors are suffixed with Channel, for example:

const theme = extendTheme();
const light = theme.colorSchemes.light;

console.log(light.palette.primary.mainChannel); // '25 118 210'
// This token is generated from `theme.colorSchemes.light.palette.primary.main`.

You can use the channel tokens to create a translucent color like this:

const theme = extendTheme({
  components: {
    MuiChip: {
      styleOverrides: {
        root: ({ theme, ownerState }) => ({
          ...(ownerState.variant === 'outlined' &&
            ownerState.color === 'primary' && {
              backgroundColor: `rgba(${theme.vars.palette.primary.mainChannel} / 0.12)`,
            }),
        }),
      },
    },
  },
});

Don't use a comma (,) as a separator because the channel colors use empty spaces to define transparency:

`rgba(${theme.vars.palette.primary.mainChannel}, 0.12)`, // 🚫 this does not work
`rgba(${theme.vars.palette.primary.mainChannel} / 0.12)`, // ✅ always use `/`

Adding new theme tokens

You can add other key-value pairs to the theme input which will be generated as a part of the CSS theme variables:

const theme = extendTheme({
  colorSchemes: {
    light: {
      palette: {
        // The best part is that you can refer to the variables wherever you like 🤩
        gradient:
          'linear-gradient(to left, var(--mui-palette-primary-main), var(--mui-palette-primary-dark))',
        border: {
          subtle: 'var(--mui-palette-neutral-200)',
        },
      },
    },
    dark: {
      palette: {
        gradient:
          'linear-gradient(to left, var(--mui-palette-primary-light), var(--mui-palette-primary-main))',
        border: {
          subtle: 'var(--mui-palette-neutral-600)',
        },
      },
    },
  },
});

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

Then, you can access those variables from the theme.vars object:

const Divider = styled('hr')(({ theme }) => ({
  height: 1,
  border: '1px solid',
  borderColor: theme.vars.palette.border.subtile,
  backgroundColor: theme.vars.palette.gradient,
}));

Or use var() to refer to the CSS variable directly:

/* global.css */
.external-section {
  background-color: var(--mui-palette-gradient);
}

TypeScript

You must augment the theme palette to avoid type errors:

declare module '@mui/material/styles' {
  interface PaletteOptions {
    gradient: string;
    border: {
      subtle: string;
    };
  }
  interface Palette {
    gradient: string;
    border: {
      subtle: string;
    };
  }
}

Changing variable prefixes

To change the default variable prefix (--mui), provide a string to cssVarPrefix property, as shown below:

const theme = extendTheme({ cssVarPrefix: 'any' });

// the stylesheet will be like this:
// --any-palette-primary-main: ...;

To remove the prefix, use an empty string as a value:

const theme = extendTheme({ cssVarPrefix: '' });

// the stylesheet will be like this:
// --palette-primary-main: ...;

Custom styles per mode

To customize the style without creating new tokens, you can use the theme.getColorSchemeSelector utility:

const Button = styled('button')(({ theme }) => ({
  // in default mode.
  backgroundColor: theme.vars.palette.primary.main,
  color: '#fff',
  '&:hover': {
    backgroundColor: theme.vars.palette.primary.dark,
  },

  // in dark mode.
  [theme.getColorSchemeSelector('dark')]: {
    backgroundColor: theme.vars.palette.primary.dark,
    color: theme.vars.palette.primary.main,
    '&:hover': {
      color: '#fff',
      backgroundColor: theme.vars.palette.primary.dark,
    },
  },
}));

Force a specific color scheme

Specify data-mui-color-scheme="dark" to any DOM node to force the children components to appear as if they are in dark mode.

<div data-mui-color-scheme="dark">
  <Paper sx={{ p: 2 }}>
    <TextField label="Email" type="email" margin="normal" />
    <TextField label="Password" type="password" margin="normal" />
    <Button>Sign in</Button>
  </Paper>
</div>

Dark color scheme application

For an application that only has a dark mode, set the default mode to dark:

const theme = extendTheme({
  // ...
});

// remove the `light` color scheme to optimize the HTML size for server-side application
delete theme.colorSchemes.light;

function App() {
  return (
    <CssVarsProvider theme={theme} defaultMode="dark">
      ...
    </CssVarsProvider>
  );
}

For a server-side application, provide the same value to getInitColorSchemeScript():

getInitColorSchemeScript({
  defaultMode: 'dark',
});