JSFiddle - React, Tailwind, and code Playground

HTML

<div class="b-popup__overlay">
    <div class="b-popup">Hello! I'm just a Popup</div
    ><i class="b-valignfix"></i>
</div>

CSS

html,
body {
    min-height: 100%;
    font: 1em/125% Arial
    }
.b-popup__overlay {

    
    width: 100%;
    height: 100%;

    text-align: center
    }
.b-popup {
    display: inline-block;
    padding: 2em 4em;
    vertical-align: middle;
    border: .5em solid rgba(0,0,0,.1);
    border-radius: 1em;
    background: #fff
    }
.b-valignfix {
    display: inline-block;
    width: 0;
    height: 100%;
    vertical-align: middle
    }