JSFiddle - React, Tailwind, and code Playground

HTML

<p>testing</p>

<div class="overlay">
  Loading website...
</div>

CSS

.overlay{
    display: none;
    position: fixed;
    padding: 0;
    margin: 0;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, .3);
    opacity: .8;
    pointer-events: none;
}

JavaScript

$(document).ready(function() {
  $(".overlay").fadeIn();
  $(window).on('load', function() {
    $(".overlay").fadeOut();
  });

});