JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header">
	<div id="button">This is a Button
		<div class="content">
		This is the Hidden Div
		</div>
	</div>
</div>

CSS

#header #button {width:200px; background:#eee}

#header #button:hover > .content {display:block; opacity:1;}

#header #button .content:hover { display:block;}

#header #button .content {

-webkit-transition: all .3s ease .15s;
-moz-transition: all .3s ease .15s;
-o-transition: all .3s ease .15s;
-ms-transition: all .3s ease .15s;
transition: all .3s ease .15s;
	
	opacity:0;
	clear: both;
	display: none;

	top: -1px;
	left:-160px;
	padding: 8px;
	min-height: 150px;
	border-top: 1px solid #EEEEEE;
	border-left: 1px solid #EEEEEE;
	border-right: 1px solid #EEEEEE;
	border-bottom: 1px solid #EEEEEE;
	-webkit-border-radius: 0px 7px 7px 7px;
	-moz-border-radius: 0px 7px 7px 7px;
	-khtml-border-radius: 0px 7px 7px 7px;
	border-radius: 0px 7px 7px 7px;
	-webkit-box-shadow: 0px 2px 2px #DDDDDD;
	-moz-box-shadow: 0px 2px 2px #DDDDDD;
	box-shadow: 0px 2px 2px #DDDDDD;
	background: #FFF;
}