JSFiddle - React, Tailwind, and code Playground

HTML

<div class="dropdown"></div>

CSS

.dropdown {
    display:block;
    opacity:0;
    /*filter:alpha(opacity=0);*/
    /*-ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=0)";*/
    width:500px;
    height:500px;
    background:transparent url('http://www.mansys.net/_images/_global/form-sprite.png');   
    -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=0),progid:DXImageTransform.Microsoft.gradient(startColorstr=#00FFFFFF,endColorstr=#00FFFFFF)"; /* IE8 */   
    filter: alpha(opacity=0),progid:DXImageTransform.Microsoft.gradient(startColorstr=#00FFFFFF,endColorstr=#00FFFFFF);   /* IE6 & 7 */ 
}

JavaScript

$(document).ready(function() {
    $('.dropdown').mouseenter(function() {
        $(this).stop().animate({
            opacity: 1
        }, 1000);
    });
    $('.dropdown').mouseleave(function() {
        $(this).stop().animate({
            opacity: 0
        }, 1000);
    });
});