Usage with Gatsby

module.exports = {
  plugins: {
    'postcss-preset-mantine': {},
    'postcss-simple-vars': {
      variables: {
        'mantine-breakpoint-xs': '36em',
        'mantine-breakpoint-sm': '48em',
        'mantine-breakpoint-md': '62em',
        'mantine-breakpoint-lg': '75em',
        'mantine-breakpoint-xl': '88em',
      },
    },
  },
};

// src/theme.ts
import { createTheme } from '@mantine/core';

export const theme = createTheme({
  fontFamily: 'serif',
  // ... other theme override properties
});

import { ColorSchemeScript, MantineProvider } from '@mantine/core';
import { theme } from './src/theme';

export const onPreRenderHTML = ({
  getHeadComponents,
  replaceHeadComponents,
}) => {
  const headComponents = getHeadComponents();
  replaceHeadComponents([
    ...headComponents,
    <ColorSchemeScript key="color-scheme-script" />,
  ]);
};

export const wrapPageElement = ({ element }) => {
  return <MantineProvider theme={theme}>{element}</MantineProvider>;
};

// Import styles of packages that you've installed.
// All packages except `@mantine/hooks` require styles imports
import '@mantine/core/styles.css';

import { MantineProvider } from '@mantine/core';
import { theme } from './src/theme';

export const wrapPageElement = ({ element }) => {
  return <MantineProvider theme={theme}>{element}</MantineProvider>;
};

npm run develop

// Default syntax – will not work in Gatsby
import classes from './Demo.module.css';

// Gatsby syntax
import * as classes from './Demo.module.css';