JSFiddle - React, Tailwind, and code Playground

CSS

.box {
  display: inline-block;
  width: 100px;
  height: 100px;
  background: red;   
}
.box.green {
  background: green;
  -webkit-transition: background 1s;    
}

JavaScript

var $box1 = $('<div class="box">').appendTo($('body'));;
var $box2 = $('<div class="box">').appendTo($('body'));;
setTimeout(function() {
    $box1.addClass('green');
    $box1.width();
    $box2.addClass('green');
}, 2);