JSFiddle - React, Tailwind, and code Playground

HTML

<div class="black">
    <div class="message">
        This is a popup message.
    </div>
</div>

CSS

.black {
    position:absolute;
    top:0;
    bottom:0;
    left:0;
    right:0;
    background:rgba(0,0,0,.5);
}
.message {
    background:yellow;
    width:200px;
    margin:auto auto;
    padding:10px;
}