円形ボタンのハンバーガーメニュー（中央で×に変形＋白線＆黒背景）

<div class="hamburger-wrapper">
  <button class="hamburger-circle" 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: #111;
  color: #fff;
}

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

.hamburger-circle {
  width: 60px;
  height: 60px;
  border-radius: 50%;
  background-color: #222;
  border: none;
  cursor: pointer;
  position: relative;
  padding: 0;
  z-index: 10;
  display: flex;
  justify-content: center;
  align-items: center;
}

.hamburger-circle span {
  position: absolute;
  width: 30px;
  height: 3px;
  background-color: #fff;
  border-radius: 2px;
  transition: all 0.4s ease;
  transform-origin: center;
}

.hamburger-circle span:nth-child(1) {
  top: 18px;
}
.hamburger-circle span:nth-child(2) {
  top: 28px;
}
.hamburger-circle span:nth-child(3) {
  top: 38px;
}

.hamburger-circle.active span:nth-child(1) {
  transform: rotate(45deg);
  top: 28px;
}

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

.hamburger-circle.active span:nth-child(3) {
  transform: rotate(-45deg);
  top: 28px;
}

.hamburger-nav {
  display: none;
  position: absolute;
  top: 120px;
  left: 50%;
  transform: translateX(-50%);
  width: 240px;
  background: #222;
  border: 1px solid #444;
  box-shadow: 0 2px 8px rgba(255,255,255,0.1);
}

.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: #fff;
}

.hamburger-nav ul li a:hover {
  background: #333;
}

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