JSFiddle - React, Tailwind, and code Playground

HTML

This is some stuff

<div class='PopupPanelBG'>
    <div class='PopupPanel'>
        <div>
            <div style='width: 1000px;'>some stuff that is really big</div>
        </div>
    </div>
</div

CSS

.PopupPanelBG {
	display: table;
	background: rgba(0, 0, 0, 0.7);
	position: fixed;
	left: 0;
	top: 0;
	width: 100%;
	height: 100%;
	z-index: 1000;
    overflow: hidden;
}

.PopupPanel {
	display: table-cell;
	vertical-align: middle;
	text-align: center;
	position: relative;
}

.PopupPanel>div {
	display: inline-block;
	vertical-align: middle;
	text-align: center;
	opacity: 0.9;
	background-color: #e1efbb;
	border: 1px solid gray;
	padding: 8px;
	margin: 30px;
	overflow : auto;
}