JSFiddle - React, Tailwind, and code Playground

HTML

<div id="menu">
  <ul>
    <li><a href="">1</a>
      <div>
        <ul>
          <li><a href="">2</a></li>
          <li><a href="">3</a></li>
        </ul>
      </div>
    </li>
  </ul>
</div>

CSS

* {
  margin: 0;
  padding: 0;
}

#menu {
  width: 50%;
  margin: 10px;
  background: #bd2323;
  text-align: center;
}

#menu ul > li {
  display: block;
  border-top: 1px solid #751313;
  position: relative;
}

#menu ul > li > a {
  display: block;
  padding: 10px 0;
  color: #FFF;
  font-size: 13px;
}

#menu ul > li > a:hover {
  background: #921d1d;
}

#menu ul > li > div > ul {
  opacity:0;
  pointer-events:none;
  transition: all 0.4s ease;
  position: absolute;
  width: 100%;
}

#menu ul > li > div > ul > li {
  border-top: 1px solid #000;
}

#menu ul > li > div > ul > li a {
  font-size: 11px;
  display: block;
}

#menu ul > li > div > ul > li a:hover {
  background: #454545;
}

#menu ul > li:hover > div > ul {
  opacity:1;
  pointer-events:all;
  background: #191919;
  transition: all 0.4s ease;
}