JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#">Hover here</a>
<div>Show me now!</div>

CSS

div {
    width: 100px; 
    height: 100px; 
    background: red; 
    margin: 20px;
    -webkit-opacity: 0;
    -moz-opacity: 0;
    -ms-opacity: 0;
    -o-opacity: 0;
    opacity: 0;
    -webkit-transition: opacity 300ms;
    -moz-transition: opacity 300ms;
    -ms-transition: opacity 300ms;
    -o-transition: opacity 300ms;
    transition: opacity 300ms;
    -webkit-transition-delay: 300ms;
    -moz-transition-delay: 300ms;
    -ms-transition-delay: 300ms;
    -o-transition-delay: 300ms;
    transition-delay: 300ms;
}

a {
    font-size: 16px; 
    font-weight: bold;
}

a:hover + div {
    -webkit-opacity: 1;
    -moz-opacity: 1;
    -ms-opacity: 1;
    -o-opacity: 1;
    opacity: 1;
}