index.html

<!DOCTYPE html>
<html lang="en">
<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">
  <title>Niver</title>
  <link rel="stylesheet" href="style.css">
</head>
<body>
  <div class="invitation">
    <div class="envelope">
      <div class="mask">
        <div class="card">
          <div class="front">
            <h1>
              <img src="invite.jpeg">
            </h1>
          </div>
        </div>
      </div>
      <div class="flap"></div>
      <button>Você recebeu um convite!<br>Clique aqui!</button>
    </div>
  </div>
</body>
<script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.19.0/TweenMax.min.js"></script>
<script src="main.js"></script>
</html>