JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
    <div class="animate start">wheeee!</div>
</div>

CSS

.animate.start {
    display: inline-block;
    height: 20px;
    background-color: green;
    color: white;
    -webkit-transition: all 0.2s ease-out;
}

.animate.start:hover {
    width: 100%;
}

#wrapper {
    margin-right: 30px;
}