JSFiddle - React, Tailwind, and code Playground

HTML

<div>Este é o conteúdo normal!</div>
<div id="preload">
    <img src="http://sierrafire.cr.usgs.gov/images/loading.gif" alt="">
</div>

CSS

#preload {
    background-color: #fff;
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%
}

JavaScript

$(document).ready(function () {
    //Esconde preloader
    $(window).load(function () {
        $("#preload").animate({
            opacity: 0
        }, 4000, function () {
            this.remove();
        });
    });
});