向下拉导航栏添加大括号

<nav>
  <ul>
    <li><a href="#">菜单1</a></li>
    <li class="has-submenu">
      <a href="#">菜单2</a>
      <ul class="submenu">
        <li><a href="#">子菜单1</a></li>
        <li><a href="#">子菜单2</a></li>
        <li><a href="#">子菜单3</a></li>
      </ul>
    </li>
    <li><a href="#">菜单3</a></li>
  </ul>
</nav>

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

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

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

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

.submenu {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background-color: #fff;
  padding: 10px;
  border: 1px solid #ccc;
}

.submenu li {
  display: block;
}

.submenu li a {
  padding: 5px 0;
}