JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    Example fade in/out
</div>

CSS

div#container{
   opacity: 1;
   transition: opacity .25s ease-in-out;
   -webkit-transition: opacity .25s ease-in-out;
   -moz-transition: opacity .25s ease-in-out;
   background-color:royalblue;
   padding:15px;
}

div#container:hover{
    opacity: 0.1;
}