JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script src="//ajax.googleapis.com/ajax/libs/mootools/1.4.5/mootools-yui-compressed.js"></script>
<div id="sobreCamada">
    <p id="lblAviso">Operação completa!</p>
</div>

CSS

#lblAviso {
    position: fixed;
    top: 50%;
    left: 50%;
    color:#000;
    font-size: 30px;
}
#sobreCamada {
    display:none;
    background-color: grey;
    opacity: 0.8;
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 1000;
    background-color:#0aa;
}

JavaScript

document.id('sobreCamada').fade('in');
setTimeout(function () {
    $('#sobreCamada').fadeIn().delay(1000).fadeOut(function () {
        $(this).remove()
    });
}, 2000);