JSFiddle - React, Tailwind, and code Playground

HTML

<div id="modal">
    <div class="center">CENTRE THIS</div>
</div>

CSS

#modal {
    background: none repeat scroll 0 0 gray;
    color: white;
    float: left;
    height: 100vh;
   
    position: relative;
    width: 100%;
}
.center {
    background-color: #444;
    height: 30px;
    left: 50%;
    line-height: 30px;
    margin-left: -56px;
    margin-top: -15px;
    position: absolute;
    text-align: center;
    top: 50%;
    width: 112px;
}