react-playground/node_modules/@mui/material/esm/styles/createMixins.js

export default function createMixins(breakpoints, mixins) {
  return {
    toolbar: {
      minHeight: 56,
      [breakpoints.up('xs')]: {
        '@media (orientation: landscape)': {
          minHeight: 48
        }
      },
      [breakpoints.up('sm')]: {
        minHeight: 64
      }
    },
    ...mixins
  };
}