index.js

import React from 'react'

export default class ServerStyled extends React.Component {
  constructor (props) {
    super(props)
    const isServer = typeof document === 'undefined'
    if (!isServer) return

    const { ServerStyleSheet } = require('styled-components')
    const { renderToString } = require('react-dom/server')
    const sheet = new ServerStyleSheet()
    renderToString(
      sheet.collectStyles(props.children)
    )
    this.styles = sheet.getStyleElement()
  }

  render () {
    if (!this.styles) return this.props.children

    return (
      <React.Fragment>
        {this.styles}
        {this.props.children}
      </React.Fragment>
    )
  }
}