JSFiddle - React, Tailwind, and code Playground

HTML

<div id="page_expander"></div>
<div id="overlay">Paused</div>

CSS

#overlay {
    background: rgba(0,0,0,0.5);
    position:fixed;
    top:50px; left:50px; right:50px; bottom:50px;
    display: none;
}

JavaScript

overlay = document.getElementById('overlay');
page_expander = document.getElementById('page_expander');

overlay.onclick = function () {
    document.body.style.overflow = ''
    overlay.style.display = 'none';
};

page_expander.onclick = function () {
    document.body.style.overflow = 'hidden'
    overlay.style.display = 'block';
};

var j = 1000, s = '';
while (--j) s = s + '<br/>' + j;
document.getElementById('page_expander').innerHTML = s;