JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<head>
<meta http-equiv="Content-type" content="text/html"; charset="UTF-8">
<link rel="stylesheet" href="list.css">
<title>Заголовок</title>
</head>
<body>
<ul id="menu">
	<li>Меню
		<ul id="sub">
			<li>О нас</li>
		</ul>
	</li>
</ul>
</body>
</html>

CSS

#menu{
    list-style-type: none;
}    
}
#sub{
	opacity: 0;
}

#menu li:hover > #sub{
	position: absolute;
	transition: 0.4s;
	transform: translate(0, 10px);
	opacity: 1;
    list-style: none;
}