バウンスアニメーション付きハンバーガーメニュー（ふわっと×に変形）

<div class="hamburger-wrapper">
  <button class="hamburger-bounce" id="hamburger-btn">
    <span></span>
    <span></span>
    <span></span>
  </button>
  <nav class="hamburger-nav" id="hamburger-nav">
    <ul>
      <li><a href="#">TOP</a></li>
      <li><a href="#">SERVICE</a></li>
      <li><a href="#">WORKS</a></li>
      <li><a href="#">CONTACT</a></li>
    </ul>
  </nav>
</div>

body {
  margin: 0;
  padding: 0;
  background: #fff;
}

.hamburger-wrapper {
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
  padding: 40px 0;
}

.hamburger-bounce {
  width: 50px;
  height: 50px;
  background: none;
  border: none;
  cursor: pointer;
  position: relative;
  padding: 0;
  z-index: 10;
}

.hamburger-bounce span {
  position: absolute;
  width: 100%;
  height: 4px;
  background-color: #ff5722;
  border-radius: 2px;
  left: 0;
  transition: transform 0.4s cubic-bezier(0.68, -0.55, 0.27, 1.55),
              opacity 0.2s ease;
  transform-origin: center;
}

.hamburger-bounce span:nth-child(1) {
  top: 12px;
}
.hamburger-bounce span:nth-child(2) {
  top: 23px;
}
.hamburger-bounce span:nth-child(3) {
  top: 34px;
}

.hamburger-bounce.active span:nth-child(1) {
  transform: rotate(45deg);
  top: 23px;
}

.hamburger-bounce.active span:nth-child(2) {
  opacity: 0;
}

.hamburger-bounce.active span:nth-child(3) {
  transform: rotate(-45deg);
  top: 23px;
}

.hamburger-nav {
  display: none;
  position: absolute;
  top: 120px;
  left: 50%;
  transform: translateX(-50%);
  width: 240px;
  background: #fff;
  border: 1px solid #ddd;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.hamburger-nav.open {
  display: block;
}

.hamburger-nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

.hamburger-nav ul li a {
  display: block;
  padding: 14px 18px;
  text-decoration: none;
  color: #333;
}

.hamburger-nav ul li a:hover {
  background: #f7f7f7;
}

document.getElementById("hamburger-btn").addEventListener("click", function() {
  this.classList.toggle("active");
  document.getElementById("hamburger-nav").classList.toggle("open");
});