message: just output the transcluded CSS in StyleProvider
diff: import React from 'react'
  -import PropTypes from 'prop-types'
  -import {theme} from '../../src'
  +import css from './css'
  +export default function StyleProvider(props) {
  /* eslint-disable-next-line react/no-danger */
  -const Styles = ({css}) => <style dangerouslySetInnerHTML={{__html: css}} />
  -
  -const fonts = theme.fonts.map(name => (name.indexOf(' ') > -1 ? `"${name}"` : name)).join(', ')
  -
  -Styles.defaultProps = {
  - css: `
  - * { box-sizing: border-box; }
  - body {
  - margin: 0;
  - font-family: ${fonts};
  - line-height: ${theme.lineHeight};
  - }
  - `
  + return <style {...props} dangerouslySetInnerHTML={{__html: css}} />
  }
  -
  -Styles.propTypes = {
  - css: PropTypes.string
  -}
  -
  -export default Styles
  