JSFiddle - React, Tailwind, and code Playground

HTML

<div id="overlay"></div>
<input type="button" value="click">

CSS

#overlay {
    background-color: rgba(0, 0, 0, 0.8);
    z-index: 999;
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    display: none;
}

JavaScript

$(":button").click(function() {
    $("#overlay").show();
});

$("#overlay").click(function() {
    $(this).hide();
});