templates/404.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <link
      rel="stylesheet"
      href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css"
      integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh"
      crossorigin="anonymous"
    />
    <link
      rel="stylesheet"
      href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.1/css/all.min.css"
    />
    <style>
      body {
        width: 100vw;
        height: 100vh;
        overflow: hidden;
      }

      #authentication-status {
        font-size: 3em;
        display: table;
        visibility: visible;
        overflow: hidden;
        width: 100%;
        height: 100%;
      }

      #authentication-status .info {
        font-size: 0.4em;
      }
      #authentication-status .timer {
        font-size: 0.3em;
      }

      .alert {
        visibility: hidden;
        text-align: center;
      }
    </style>

    <script language="JavaScript" type="text/javascript">
      var time = 6;

      function startTimer() {
        if (time <= 0) {
          window.location =
            "https://github.com/Abhijeet-AR/Competitive_Programming_Score_API";
          return;
        } else {
          time--;
          document.getElementById("timer").innerHTML =
            "Redirecting to GitHub in " + time + " seconds";
          setTimeout(startTimer, 1000);
        }
      }

      window.onload = startTimer;
    </script>
    <title>NOT FOUND</title>
  </head>
  <body>
    <div class="alert alert-danger" id="authentication-status" role="alert">
      <div style="display: table-cell; vertical-align: middle;">
        <div>Error 404: PAGE NOT FOUND</div>
        <div class="info">
          Check
          <a
            href="https://github.com/Abhijeet-AR/Competitive_Programming_Score_API"
            style="color: inherit;"
            >this <i class="fab fa-github"></i> GitHub Repository</a
          >
          for usage instructions
        </div>
        <div class="timer" id="timer"></div>
      </div>
    </div>
  </body>
</html>