Globals

The overrides key enables you to customize the appearance of all instances of a component type, while the props key enables you to change the default value(s) of a component's props.

CSS

When the configuration variables aren't powerful enough, you can take advantage of the overrides key of the theme to potentially change every single style injected by Material-UI into the DOM. That's a really powerful feature.

const theme = createTheme({
  overrides: {
    // Style sheet name ⚛️
    MuiButton: {
      // Name of the rule
      text: {
        // Some CSS
        color: 'white',
      },
    },
  },
});

The list of these customization points for each component is documented under the Component API section. For instance, you can have a look at the Button. Alternatively, you can always have a look at the implementation.

Global CSS

If you are using the CssBaseline component to apply global resets, it can also be used to apply global styles. For instance:

const theme = createTheme({
  overrides: {
    MuiCssBaseline: {
      '@global': {
        html: {
          WebkitFontSmoothing: 'auto',
        },
      },
    },
  },
});

// ...
return (
  <ThemeProvider theme={theme}>
    <CssBaseline />
    {children}
  </ThemeProvider>
);

Default props

You can change the default props of all the Material-UI components. A props key is exposed in the theme for this use case.

const theme = createTheme({
  props: {
    // Name of the component ⚛️
    MuiButtonBase: {
      // The default props to change
      disableRipple: true, // No more ripple, on the whole application 💣!
    },
  },
});