message: use utility and markdown css exports
diff: -/* global preval */
  import React from 'react'
  import Document, {Head, Main, NextScript} from 'next/document'
  import {ServerStyleSheet} from 'styled-components'
  import {extractCritical} from 'emotion-server'
  -import preval from 'preval.macro'
  -
  -const customCSS = preval`
  - const {renderFile} = require('../lib/render-sass')
  - const path = require.resolve('./primer-custom.scss')
  - module.exports = renderFile(path)
  -`
  +import {UtilityCSS, MarkdownCSS} from '../src'
  export default class MyDocument extends Document {
  static getInitialProps({renderPage}) {
  @@ -19,7 +12,10 @@ export default class MyDocument extends Document {
  ...page,
  styles: (
  <>
  - <style id="primer-custom">{customCSS}</style>
  + <style id="primer-css">
  + {UtilityCSS}
  + {MarkdownCSS}
  + </style>
  <style id="emotion-static">{extractCritical(page.html).css}</style>
  {sheet.getStyleElement()}
  </>
  