website/src/pages/404.tsx

import React, { Fragment } from "react"

import { SEO } from "../components/SEO"

function NotFoundPage() {
  return (
    <Fragment>
      <SEO title="404: Not found" />
      <h1>NOT FOUND</h1>
      <p>You just hit a route that doesn&#39;t exist... the sadness.</p>
    </Fragment>
  )
}

export default NotFoundPage