JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
<div class="reveal"></div>
</div>

CSS

.reveal {
    width: 400px;
    height: 400px;
    background: black;
    transition: background 1s linear;
    -webkit-transition: background 0.2s linear;
    -moz-transition: background 0.2s linear;
    -o-transition: background 0.2s linear;
}
.wrapper:hover .reveal {
    background: blue;
}
.wrapper {
    width: 500px;
    height: 500px;
    background: red;
}
}