JSFiddle - React, Tailwind, and code Playground

HTML

<div class="stubborn"></div>

CSS

div { border: 1px solid red; width: 100px; height: 100px; }

div.stubborn { display: none !important; }

div.hidden_block_el { 
   display: block !important;
   opacity: 0;
}

JavaScript

$(function () {
    $('.stubborn').addClass('hidden_block_el').animate({opacity: 1}, 2000);
});