<!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>Calculator</title>
  <link rel="stylesheet" href="./styles.scss">
  <!-- Include React and ReactDOM from CDN for simplicity. In a real project, you'd likely use npm/yarn and a build tool. -->
  <script src="https://unpkg.com/react@17/umd/react.development.js"></script>
  <script src="https://unpkg.com/react-