public/404.html

<!DOCTYPE html>
<html lang="">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width,initial-scale=1.0">
    <link rel="icon" href="<%= BASE_URL %>favicon.ico">
    <title><%= htmlWebpackPlugin.options.title %></title>
    <!-- <script>
  // ========================================
  // Credits:
  // - https://stackoverflow.com/a/50259501
  // - https://stackoverflow.com/a/50247140
  // ========================================
  const segment = 1

  sessionStorage.redirect = '/' + location.pathname.slice(1).split('/').slice(segment).join('/')

  location.replace(
    location.pathname.split('/').slice(0, 1 + segment).join('/')
  )
</script> -->
<script type="text/javascript">
// Single Page Apps for GitHub Pages
// MIT License
// https://github.com/rafgraph/spa-github-pages
// This script takes the current url and converts the path and query
// string into just a query string, and then redirects the browser
// to the new url with only a query string and hash fragment,
// e.g. https://www.foo.tld/one/two?a=b&c=d#qwe, becomes
// https://www.foo.tld/?/one/two&a=b~and~c=d#qwe
// Note: this 404.html file must be at least 512 bytes for it to work
// with Internet Explorer (it is currently > 512 bytes)

// If you're creating a Project Pages site and NOT using a custom domain,
// then set pathSegmentsToKeep to 1 (enterprise users may need to set it to > 1).
// This way the code will only replace the route part of the path, and not
// the real directory in which the app resides, for example:
// https://username.github.io/repo-name/one/two?a=b&c=d#qwe becomes
// https://username.github.io/repo-name/?/one/two&a=b~and~c=d#qwe
// Otherwise, leave pathSegmentsToKeep as 0.
var pathSegmentsToKeep = 1;

var l = window.location;
l.replace(
  l.protocol + '//' + l.hostname + (l.port ? ':' + l.port : '') +
  l.pathname.split('/').slice(0, 1 + pathSegmentsToKeep).join('/') + '/?/' +
  l.pathname.slice(1).split('/').slice(pathSegmentsToKeep).join('/').replace(/&/g, '~and~') +
  (l.search ? '&' + l.search.slice(1).replace(/&/g, '~and~') : '') +
  l.hash
);

</script>
  </head>
  <body>
    <noscript>
      <strong>We're sorry but <%= htmlWebpackPlugin.options.title %> doesn't work properly without JavaScript enabled. Please enable it to continue.</strong>
    </noscript>
    <div id="app"></div>
    <!-- built files will be auto injected -->
  </body>
</html>