How to use the @govuk-react/constants.FONT_SIZE.SIZE_14 function in @govuk-react/constants

import PropTypes from 'prop-types';
import styled from 'styled-components';
import Label from '@govuk-react/label';
import LabelText from '@govuk-react/label-text';
import ErrorText from '@govuk-react/error-text';
import HintText from '@govuk-react/hint-text';
import { FONT_SIZE, LINE_HEIGHT, NTA_LIGHT, MEDIA_QUERIES } from '@govuk-react/constants';

const StyledInput = styled('input')({
  boxSizing: 'border-box',
  fontFamily: NTA_LIGHT,
  WebkitFontSmoothing: 'antialiased',
  MozOsxFontSmoothing: 'grayscale',
  fontWeight: 400,
  textTransform: 'none',
  fontSize: FONT_SIZE.SIZE_14,
  lineHeight: LINE_HEIGHT.SIZE_14,
  [MEDIA_QUERIES.LARGESCREEN]: {
    fontSize: FONT_SIZE.SIZE_16,
    lineHeight: LINE_HEIGHT.SIZE_16,
    width: '50%',
  },
  width: '100%',
  padding: '5px 4px 4px',
});

/**
 *
 * ### Usage
 *
 * Simple
 * ```jsx

import { BLUE, WHITE } from 'govuk-colours';
import {
  FONT_SIZE,
  LINE_HEIGHT,
  MEDIA_QUERIES,
  NTA_LIGHT,
} from '@govuk-react/constants';
import { withWhiteSpace } from '@govuk-react/hoc';

const StyledBadge = styled('strong')({
  display: 'inline-block',
  margin: '0 8px 0 0',
  padding: '2px 5px',
  fontFamily: NTA_LIGHT,
  fontWeight: 700,
  fontSize: FONT_SIZE.SIZE_14,
  lineHeight: LINE_HEIGHT.SIZE_14,
  textTransform: 'uppercase',
  letterSpacing: '1px',
  textDecoration: 'none',
  color: WHITE,
  backgroundColor: BLUE,
  WebkitFontMmoothing: 'antialiased',
  MozOsxFontSmoothing: 'grayscale',
  [MEDIA_QUERIES.LARGESCREEN]: {
    fontSize: FONT_SIZE.SIZE_16,
    lineHeight: LINE_HEIGHT.SIZE_16,
    paddingBottom: 0,
  },
});

/**

const TopNavWrapper = styled('div')(({ bgColor, color }) => ({
  display: 'flex',
  justifyContent: 'center',
  backgroundColor: bgColor,
  color,
  fontFamily: NTA_LIGHT,
  fontWeight: 400,
  fontSize: FONT_SIZE.SIZE_14,
  lineHeight: LINE_HEIGHT.SIZE_14,
  [MEDIA_QUERIES.LARGESCREEN]: {
    fontSize: FONT_SIZE.SIZE_16,
    lineHeight: LINE_HEIGHT.SIZE_16,
  },
}));

height: nextPage ? '13px' : undefined,
        width: nextPage ? '17px' : undefined,
        marginLeft: nextPage ? '10px' : undefined,
      },
    },
  }),
);

const InnerWrap = styled('div')({
  display: 'flex',
  alignItems: 'center',
  width: '100%',
});

const PageTitle = styled('span')({
  fontSize: FONT_SIZE.SIZE_14,
  lineHeight: LINE_HEIGHT.SIZE_14,
  textDecoration: 'underline',
  [MEDIA_QUERIES.LARGESCREEN]: {
    fontSize: FONT_SIZE.SIZE_16,
    lineHeight: LINE_HEIGHT.SIZE_16,
  },
});

const asPaginationItem = (AnchorType) => {
  const PaginationItem = props => (