ハンバーガー #JavaScript

<!DOCTYPE html>
<html lang="ja">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>My Site</title>
  <link href="https://fonts.googleapis.com/icon?family=Material+Icons" rel="stylesheet">
  <link rel="stylesheet" href="css/styles.css">
  <style>
body {
  margin: 0;
  font-family: Verdana, sans-serif;
}

header {
  display: flex;
  padding: 0 16px;
}

header h1 {
  margin: 0;
  font-size: 22px;
  line-height: 64px;
}

.sp-menu {
  margin-left: auto;
}

.sp-menu #open {
  font-size: 32px;
  line-height: 64px;
  cursor: pointer;
}

.sp-menu #open.hide {
  display: none;
}

main {
  padding: 0 16px;
}

.overlay {
  position: fixed;
  top: 0;
  bottom: 0;
  right: 0;
  left: 0;
  background: rgba(255, 255, 255, 0.95);
  text-align: center;
  padding: 64px;
  opacity: 0;
  pointer-events: none;
  transition: opacity .6s;
}

.overlay.show {
  opacity: 1;
  pointer-events: auto;
}

.overlay #close {
  position: absolute;
  top: 16px;
  right: 16px;
  font-size: 32px;
  cursor: pointer;
}

.overlay ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
}

.overlay li {
  margin-top: 24px;
  opacity: 0;
  transform: translateY(16px);
  transition: opacity .3s, transform .3s;
}

.overlay.show li {
  opacity: 1;
  transform: none;
}

.overlay.show li:nth-child(1) {
  transition-delay: .1s;
}

.overlay.show li:nth-child(2) {
  transition-delay: .2s;
}

.overlay.show li:nth-child(3) {
  transition-delay: .3s;
}

.pc-menu {
  display: none;
}

@media (min-width: 600px) {
  .pc-menu {
    display: block;
    margin-left: auto;
  }

  .pc-menu ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    display: flex;
  }

  .pc-menu a {
    display: block;
    width: 80px;
    line-height: 64px;
    text-align: center;
  }

  .pc-menu a:hover {
    background: #f2f2f2;
  }

  .sp-menu {
    display: none;
  }
}
  </style>
</head>
<body>
  <header>
    <div class="logo">
      <h1>LOGO</h1>
    </div>

    <div class="pc-menu">
      <nav>
        <ul>
          <li><a href="#">Menu</a></li>
          <li><a href="#">Menu</a></li>
          <li><a href="#">Menu</a></li>
        </ul>
      </nav>
    </div>

    <div class="sp-menu">
      <span class="material-icons" id="open">menu</span>
    </div>
  </header>

  <div class="overlay">
    <span class="material-icons" id="close">close</span>
    <nav>
      <ul>
        <li><a href="#">Menu</a></li>
        <li><a href="#">Menu</a></li>
        <li><a href="#">Menu</a></li>
      </ul>
    </nav>
  </div>

  <main>
    <p>こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。</p>
    <p>こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。こんにちは。</p>
  </main>

  <script>
    {
  const open = document.getElementById('open');
  const overlay = document.querySelector('.overlay');
  const close = document.getElementById('close');

  open.addEventListener('click', () => {
    overlay.classList.add('show');
    open.classList.add('hide');
  });

  close.addEventListener('click', () => {
    overlay.classList.remove('show');
    open.classList.remove('hide');
  });
}
  </script>
</body>
</html>