如何让下拉导航栏与html和css一起工作？

<nav>
  <ul>
    <li><a href="#">首页</a></li>
    <li>
      <a href="#">产品</a>
      <ul>
        <li><a href="#">产品1</a></li>
        <li><a href="#">产品2</a></li>
        <li><a href="#">产品3</a></li>
      </ul>
    </li>
    <li><a href="#">关于我们</a></li>
    <li><a href="#">联系我们</a></li>
  </ul>
</nav>

nav {
  background-color: #f0f0f0;
  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;
  color: #333;
  text-decoration: none;
}

nav ul ul {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background-color: #f0f0f0;
}

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

nav ul ul li {
  width: 100%;
}

nav ul ul li a {
  padding: 10px;
  color: #333;
}

nav ul ul ul li {
  position: relative;
  top: -60px;
  left: 100%;
}