js ul菜单样式

<ul class="menu">
  <li><a href="#">首页</a></li>
  <li class="has-submenu"><a href="#">服务</a>
    <ul class="submenu">
      <li><a href="#">服务1</a></li>
      <li><a href="#">服务2</a></li>
    </ul>
  </li>
  <li><a href="#">关于我们</a></li>
</ul>

.menu {
  list-style: none;
  padding: 0;
  display: flex;
}

.menu > li {
  position: relative;
}

.menu a {
  display: block;
  padding: 10px 20px;
  text-decoration: none;
  color: #333;
}

.menu .submenu {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background-color: #fff;
  box-shadow: 0 2px 5px rgba(0,0,0,0.2);
  min-width: 150px;
}

.menu .submenu li a {
  padding: 10px;
}

.menu li:hover .submenu {
  display: block;
}

document.querySelectorAll('.has-submenu').forEach(function(menuItem) {
  menuItem.addEventListener('mouseenter', function() {
    this.querySelector('.submenu').style.display = 'block';
  });
  menuItem.addEventListener('mouseleave', function() {
    this.querySelector('.submenu').style.display = 'none';
  });
});