JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box"></div>

CSS

.box {
    width: 200px; height: 100px;
    background-size: 100% 200%;
    background-image: linear-gradient(to bottom, red 50%, black 50%);
    -webkit-transition: background-position 1s;
    -moz-transition: background-position 1s;
    transition: background-position 1s;
}

.box:hover {
    background-position: 0 -100%;
}