docs/src/components/Layout.jsx

import React from 'react'
import PropTypes from 'prop-types'
import Header from './Header'
import Footer from './Footer'

const Layout = ({ children, header }) => {
  const headerElement = header || <Header />

  return (
    <>
      {headerElement}
      {children}
      <Footer />
    </>
  )
}

Layout.propTypes = {
  children: PropTypes.node.isRequired,
  header: PropTypes.element
}

export default Layout