我想在导航栏中的某个类别下创建一个下拉子类别

<nav>
  <ul>
    <li><a href="#">类别1</a>
      <ul>
        <li><a href="#">子类别1.1</a></li>
        <li><a href="#">子类别1.2</a></li>
        <li><a href="#">子类别1.3</a></li>
      </ul>
    </li>
    <li><a href="#">类别2</a>
      <ul>
        <li><a href="#">子类别2.1</a></li>
        <li><a href="#">子类别2.2</a></li>
        <li><a href="#">子类别2.3</a></li>
      </ul>
    </li>
    <li><a href="#">类别3</a></li>
  </ul>
</nav>

nav {
  background-color: #f2f2f2;
  padding: 10px;
}

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

nav ul li {
  display: inline-block;
  position: relative;
}

nav ul li a {
  display: block;
  padding: 10px;
  text-decoration: none;
  color: #333;
}

nav ul li ul {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background-color: #fff;
  padding: 10px;
}

nav ul li:hover ul {
  display: block;
}

nav ul li ul li {
  display: block;
}

// 使用原生JavaScript实现
var navItems = document.querySelectorAll('nav ul li');

for (var i = 0; i < navItems.length; i++) {
  navItems[i].addEventListener('mouseover', function() {
    this.querySelector('ul').style.display = 'block';
  });

  navItems[i].addEventListener('mouseout', function() {
    this.querySelector('ul').style.display = 'none';
  });
}