JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a">a
    <div id="b">
        <img src="http://placekitten.com/300/301"/>
    </div>
</div>

CSS

#a{
    width:50px;
    height:50px;
    background-color:green;
    transition:0s 100s;
}

#b{
    width:200px; 
    height:200px;
    opacity:0;
    transition:0s 100s;
}

#a:hover #b{
    opacity:1;
    transition:0s;
}