CSS导航栏-菜单选项不会停留在导航栏中

<nav>
  <ul>
    <li><a href="#">菜单1</a></li>
    <li><a href="#">菜单2</a></li>
    <li><a href="#">菜单3</a></li>
    <li><a href="#">菜单4</a></li>
  </ul>
</nav>

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

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

nav a {
  display: block;
  padding: 10px;
  text-decoration: none;
  color: #000;
}

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

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

nav ul ul li {
  width: 200px;
  float: none;
  display: list-item;
  position: relative;
}

nav ul ul ul li {
  position: relative;
  top: -60px;
  left: 200px;
}

nav li:hover {
  background-color: #f1f1f1;
}

nav li:hover a {
  color: #000;
}

nav li:hover ul ul {
  display: none;
}

nav li:hover ul {
  display: block;
}