Material-ui: Too small font in react app with typescript example

I've based my app on https://github.com/mui-org/material-ui/tree/v1-beta/examples/create-react-app-with-typescript

I'm trying to include very basic navbar:

const styles: StyleRulesCallback<'root'> = theme => ({
  root: {
    textAlign: 'center',
    paddingTop: theme.spacing.unit * 20,
  },
});

class App extends React.Component<WithStyles<'root'>, {}> {

  render() {
    return (
      <div className={this.props.classes.root}>

          <AppBar>
            <Toolbar>
              <Typography variant="title" color="inherit">
                 Title
              </Typography>
            </Toolbar>
          </AppBar>

      </div>
    );
  }
}

export default withRoot(withStyles(styles)<{}>(App));

It seems like all the fonts in material ui components are small. buttons, select, typograhy.

For example, why I see this:

instead of https://material-ui-next.com/demos/app-bar/

I mean why is the font so small?