@material-ui/stylesでtypographyのstylesを変更


./components/ui/Theme.js
import { createMuiTheme } from "@material-ui/core/styles";

export default createMuiTheme({
  palette: {
    primary: {
      main: "#19448e",
    },
  },
  typography: {
    h3: {
      fontWeight: 300,
    },
  },
});

./components/ui/Theme.js
import { createMuiTheme } from "@material-ui/core/styles";

export default createMuiTheme({
  palette: {
    primary: {
      main: "#19448e",
    },
  },
  typography: {
    h3: {
      fontWeight: 600,
    },
  },
});