JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" value="button 1"/>
<input type="button" style="position: absolute; top: 800px;" value="button 2"/>

<div class="overlay"></div>

CSS

.overlay
{
    display: none;
    position: fixed;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    width: 100%;
    height: 100%;
    z-index: 1000;
    background-color: #909090;
    filter: alpha(opacity=50);
    -moz-opacity: 0.5;
    -khtml-opacity: 0.5;
    opacity: 0.5;
}

JavaScript

$('.overlay').show();