Responsive Typography in Material UI?

Designs commonly have smaller headline fonts for mobile designs.

Does Material UI have a mechanism for making the typography responsive?

I see that the default theme has the font sizes defined in rems - does that mean it's a matter of just reducing the base font-size? (That doesn't seem to work, what if you want to reduce the headline fonts at different rates).

Update

MUI v4 has responsive typography built in! Check here for details.

Old response

@Luke's answer is great. I wanted to add some detail to make this work in practice, because both breakpoints and pxToRem are accessible on the theme object... making this becomes a chicken and egg problem! My approach:

import { createMuiTheme } from "@material-ui/core"

const defaultTheme = createMuiTheme({ ... customisations that don’t rely on theme properties... })
const { breakpoints, typography: { pxToRem } } = defaultTheme

const theme = {
  ...defaultTheme,
  overrides: {
    MuiTypography: {
      h1: {
        fontSize: "5rem",
        [breakpoints.down("xs")]: {
          fontSize: "3rem"
        }
      }
    }
  }
}

export default theme