JSFiddle - React, Tailwind, and code Playground

HTML

<div class="background">
    1<br>2<br>3<br>4<br>5<br>6<br>
    <div class="overlay">
        <div>foobar</div>
    </div>
</div>

CSS

.background
{
    border: 1px solid black;
    position: relative;
}

.overlay
{
    position: absolute;
    top: 50%;
    left: 50%;
}

.overlay > div
{
    background: #888;
    color: #fff;
    position: relative;
    top: -50%;
    left: -50%;
    padding: 10px;
}