JSFiddle - React, Tailwind, and code Playground

HTML

<style>.loading-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, .6);
}
.loading {
    font-size: 20px;
    text-align: center;
    color: #FFF;
    position: absolute;
    top: 50%;
    left: 0;
    width: 100%;
}</style>
<div class="loading-overlay" id="loading">
    <div class="loading">Loading..</div>
</div>

JavaScript

setTimeout(function() {
    document.getElementById('loading').style.display = 'none';
}, 3000)