如何在顶部栏中居中显示菜单？

<div class="top-bar">
  <ul class="menu">
    <li><a href="#">菜单项1</a></li>
    <li><a href="#">菜单项2</a></li>
    <li><a href="#">菜单项3</a></li>
  </ul>
</div>

.top-bar {
  width: 100%;
  height: 50px;
  background-color: #f2f2f2;
  border-bottom: 1px solid #ccc;
}

.menu {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 100%;
  height: 100%;
  padding: 0;
  margin: 0;
}

.menu li {
  list-style: none;
  margin-right: 20px;
}

.menu li:last-child {
  margin-right: 0;
}

.menu li a {
  text-decoration: none;
  color: #333;
}