JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <span>Наведи</span>
  <div>Мяу</div>
</div>

CSS

*,
:before,
:after {
  box-sizing: border-box;
}

body {
  margin: 0;
  text-align: center;
  font-family: sans-serif;
}


body>div {
  margin: 30px auto;
  width: 100%;
  max-width: 300px;
  padding: 10px 15px;
  border-radius: 10px;
  box-shadow: 0 0 10px 0 #999;
  background-color: #fff;
  position: relative;
  transition: border-radius .2s;
}

body>div>div {
  position: absolute;
  top: 100%;
  left: 0;
  width: 100%;
  padding: 10px 15px;
  border-radius: 10px;
  box-shadow: 0 0 10px 0 #999;
  background: #333;
  border-radius: 0 0 10px 10px;
  color: #fff;
  transform: translateY(-50%); /* Задаём изначально */ 
  opacity: 0;
  visibility: hidden;
  transition: transform .2s, opacity .2s, visibility .2s;
}

body>div:hover {
  border-radius: 10px 10px 0 0;
}

body>div:hover>div {
  transform: none; /* Убираем его при наведении */ 
  opacity: 1;
  visibility: visible;
}