index.html

<!DOCTYPE html>
<html lang="en">
<head>
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <meta http-equiv="X-UA-Compatible" content="ie=edge">
   <title>JavaScript Calculator</title>
   <link rel="stylesheet" href="css/normalize.css">
   <link rel="stylesheet" href="css/style.css">
   <link rel="shortcut icon" href="favicon.ico">
   <link rel="shortcut icon" href="favicon.png">
</head>
<body>
   
   <div class="wrapper">

      <form id="calculator__form">
         <input type="number" requried>
         <select name="operation" id="operation__select" required>
            <option value="add">+</option>
            <option value="subtract">-</option>
            <option value="multiply">&times;</option>
            <option value="divide">&divide;</option>
            <!-- Add your own operation here! -->
         </select>
         <input type="number" requried>
         <button>=</button>
         <input type="number" id="operation__result" disabled>
      </form>

   </div>

   <script src="js/script.js"></script>
</body>
</html>