JSFiddle - React, Tailwind, and code Playground

HTML

<div id="block"></div>

CSS

#block {width: 100%; height: 2000px; background: #000;}
#block.animated {
  height: 200px;
  -webkit-transition: all 5s ease;
  -o-transition: all 5s ease;
  -ms-transition: all 5s ease;
  -moz-transition: all 5s ease;
  transition: all 5s ease;
}

JavaScript

$(document).ready(function() {
    setTimeout (function() {
        $('#block').addClass('animated');
    },500)
});