JSFiddle - React, Tailwind, and code Playground
HTML
<div class="main">
<div class="box"></div>
</div>CSS
.main{ height:300px; border:1px red solid;position:relative}
.box{width:40px; height:40px; background:red; }
/* for centering */
.box{ display: inline-block;position:relative; top:50%; margin-top:-20px; }
.main{ text-align: center; }