JSFiddle - React, Tailwind, and code Playground

HTML

<div id='cont'>
    <div id='opacity'></div>
    <div id='body'></div>
</div>

CSS

#body, #opacity  {
    width: 128px;
    height: 128px;
    z-index:2;
    position: relative;
    background: url('http://sverstay-ka.ru/plugins/backgroundImageTransition/style/img/css.png');
}
#opacity {
    position: absolute;
    opacity: 0;
    z-index:3;
    background: url('http://sverstay-ka.ru/plugins/backgroundImageTransition/style/img/css_h.png');
    transition: opacity 0.3s  ;
}
#opacity:hover {
    opacity: 1;    
}