JSFiddle - React, Tailwind, and code Playground

CSS

#lblAviso {
    position: fixed;
    top: 50%;
    left: 50%;
    color:#000;
    font-size: 30px;
}
#sobreCamada {
    display:none;
    background-color: grey;
    opacity: 0.5;
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 1000;
    background-color:#0aa;
}

JavaScript

var sobreCamada = $('<div id="sobreCamada"><p id="lblAviso">Salvo com sucesso</p></div>');

//codigo que vocĂŞ quer:
$(document.body).append(sobreCamada);
$('#sobreCamada').fadeIn().delay(3000).fadeOut(function () {
    $(this).remove()
});