JSFiddle - React, Tailwind, and code Playground

HTML

<div id="blah" style="color:#fff; opacity:1; background:black; height:50px; position:relative; ">fsdljfdsjfds</div>
<a id="click" href="#">fjsd</a>

JavaScript

$.fn.customFadeOut = function(callback) {
  var el = this;
  return $(this).animate({
    opacity: 0.25,
    fontSize: "3em", 
    height: 'toggle'
  }, 5000, function() {
     callback.apply(this)
  });

  }
                  
                  $('#click').click(function() {
                      alert('k')
                      $('#blah').customFadeOut(function() {
                          alert('god')
                              
                              })
                              
                              })