JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrap" id="menu">
  <ul class="parent">
    <li class="parent-item">菜单1</li>
    <li class="parent-item">菜单2</li>
    <li class="parent-item">菜单3</li>
    <li class="parent-item">菜单4</li>
    <li class="parent-item">菜单5</li>
    <li class="parent-item">菜单6</li>
  </ul>
  <ul class="child-wrap" id="childMenu">
    <li class="child-item">
        <ul class="">
          <li class="parent-item">菜单1</li>
          <li class="parent-item">菜单2</li>
          <li class="parent-item">菜单3</li>
          <li class="parent-item">菜单4</li>
          <li class="parent-item">菜单5</li>
          <li class="parent-item">菜单6</li>
        </ul>
    </li>
    <li class="child-item">
      <h1>子菜单2</h1>
    </li>
    <li class="child-item">
      <h1>子菜单3</h1>
    </li>
    <li class="child-item">
      <h1>子菜单4</h1>
    </li>
    <li class="child-item">
      <h1>子菜单5</h1>
    </li>
    <li class="child-item">
      <h1>子菜单6</h1>
    </li>
  </ul>
</div>

CSS

*{margin:0;padding:0;list-style:none;}

.wrap {
  position: relative;
  margin: 20px;
  width: 500px;
  font-size: 14px;
}

.parent{
  position: relative;
  z-index: 2;
  width: 200px;
  background: #eee;
  color: #666
}

.parent-item {
  line-height: 28px;
  text-align: center;
  border: 1px solid transparent;
  border-right: none;
}
.parent-item.hover {
  margin-right: -1px;
  padding-right: 1px;
  background: #fff;
  border-color: #ddd;
}
.child-wrap {
  display: none;
  position: absolute;
  top: 0;
  left: 200px;
  z-index: 1;
  height: 100%;
  border: 1px solid #ddd;
  background: #fff;
}
.child-item {
  display: none;
  width: 300px;
  height: 100%;
  text-align: center;
}

JavaScript

var $childMenu = $('#childMenu');
$('#menu').on('mouseenter', '.parent-item', function(){
	var $this = $(this),
			index = $this.index();
  $this.addClass('hover').siblings().removeClass('hover');
  $childMenu.show().find('.child-item').hide().eq(index).show();
}).on('mouseleave', function(){
	$(this).find('.parent-item.hover').removeClass('hover');
  $childMenu.hide();
})