public/404.html

<!DOCTYPE html>
<html>
<head>
  <title>The page you were looking for doesn't exist (404)</title>
  <meta name="viewport" content="width=device-width,initial-scale=1">
  <style>
    .not-found-page {
      height: 100vh;
      min-height: 500px;
    }
    .tv__outer {
      display: table;
      position: absolute;
      height: 98%;
      width: 98%;
    }

    .tv__middle {
      display: table-cell;
      vertical-align: middle;
      position: relative;
    }

    .tv__inner {
      margin-left: auto;
      margin-right: auto;
      display: table;
    }

    .tv__inner--special {
      position: absolute;
      left: 0;
      right: 0;
      margin: auto;
      -webkit-animation-name: fade;
      -webkit-animation-iteration-count: infinite;
      -webkit-animation-duration: 2s;
      animation-name: fade;
      animation-iteration-count: infinite;
      animation-duration: 2s;
    }

    .tv__inner--text {
      margin-left: auto;
      margin-right: auto;
      display: table;
      font-size: 22px;
      font-weight: 500;
    }

    .tv__inner--special, .tv__inner {
      max-width: 85%;
      width: 300px;
      border: 25px solid rgb(54, 55, 124);
      border-radius: 36px;
    }
    .tv__inner--text {
      text-align: center;
      max-width: 90%;
    }

    @-webkit-keyframes fade {
      0% {opacity: 1;}
      10% {opacity: 1;}
      20% {opacity: 0;}
      25% {opacity: 0;}
      28% {opacity: 0;}
      30% {opacity: 0;}
      33% {opacity: 1;}
      45% {opacity: 1;}
      53% {opacity: 0;}
      100% {opacity: 0;}
    }

    @keyframes fade {
      0% {opacity: 1;}
      10% {opacity: 1;}
      20% {opacity: 0;}
      25% {opacity: 0;}
      28% {opacity: 0;}
      30% {opacity: 0;}
      33% {opacity: 1;}
      45% {opacity: 1;}
      53% {opacity: 0;}
      100% {opacity: 0;}
    }
  </style>
</head>

<body>
  <div class="not-found-page base-background-color">
    <div class="tv__outer">
        <div class="tv__middle">
          <img class="tv__inner" src="https://i.imgur.com/AdvTDlI.jpg" alt="404 not found">
          <br>
          <p class="tv__inner--text">This page does not exist <br><br> <a href="/">Return to Home Page</a></p>
        </div>
      </div>
  </div>
</body>
</html>