How to use the @storybook/components.baseFonts function in @storybook/components

subtitle: _propTypes2.default.string,
  info: _propTypes2.default.string,
  chapters: _propTypes2.default.arrayOf(_propTypes2.default.object),
  addonInfo: _propTypes2.default.object
};

var defaultProps = {
  context: {},
  title: '',
  subtitle: '',
  info: '',
  chapters: []
};

var storyStyles = exports.storyStyles = {
  story: (0, _extends3.default)({}, _components.baseFonts),
  header: {
    marginBottom: 60
  },
  title: {
    color: _theme2.default.grayDarkest,
    fontSize: 36,
    marginBottom: 10
  },
  subtitle: {
    color: _theme2.default.grayDark,
    fontSize: 18,
    marginBottom: 20,
    marginTop: 0
  },
  info: _theme2.default.infoStyle
};