declarative-typography.tsx

const theme = createTheme();
theme.typography = {
  title: {
    fontSize: “40px”,
    [theme.breakpoints.down(“sm”)]: {
      fontSize: “18px”
    }
  }
};

export default function App() {
  return (
    <ThemeProvider theme={theme}>
      <Typography variant=”title”>Resize me</Typography>
    </ThemeProvider>
  );
}