JSFiddle - React, Tailwind, and code Playground

HTML

<div class="dropdown">
    <ul>
        <li>
            <a href="#">level1-link1</a>
        </li>
        <li>
            <a href="#">level1-link2</a>
            <ul>
                <li>
                    <a href="#">level2-link1</a>
                </li>
                <li>
                    <a href="#">level2-link2</a>
                    <ul>
                        <li>
                            <a href="#">level3-link1</a>
                        </li>
                        <li>
                            <a href="#">level3-link2</a>
                            <ul>
                                <li>
                                    <a href="#">level4-link1</a>
                                </li>
                                <li>
                                    <a href="#">level4-link2</a>
                                </li>
                            </ul>    
                        </li>
                    </ul>    
                </li>
            </ul>    
        </li>
        <li>
            <a href="#">level1-link3</a>
        </li>
        <li>
            <a href="#">level1-link4</a>
        </li>
        <div class="clear"></div>
    </ul>
    <div class="white_layer"></div>
</div>    
<img src="http://dev.icsandbox.com/wp-content/uploads/2015/01/Home_CloselyHeld-opt.jpg" />

CSS

/* http://meyerweb.com/eric/tools/css/reset/ 
   v2.0 | 20110126
   License: none (public domain)
*/

html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, img, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
b, u, i, center,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead, tr, th, td,
article, aside, canvas, details, embed, 
figure, figcaption, footer, header, hgroup, 
menu, nav, output, ruby, section, summary,
time, mark, audio, video
{
	margin: 0;
	padding: 0;
	border: 0;
	font-size: 100%;
	font: inherit;
	vertical-align: baseline;
}

*
{
    -moz-box-sizing: border-box;
    -webkit-box-sizing: border-box;
    box-sizing: border-box;
}

body
{
    font: 18px arial, sans-serif;
    
}

ol, ul
{
	list-style: none;
}

a
{
    text-decoration: none;
    color: #333;
}

a:hover
{
    color: #0066a4;
}

img
{
    max-width: 100%;
}

.clear
{
    clear: both;
}

.dropdown, .dropdown > ul > li
{
    position: relative;
}

.white_layer
{
    width: 100%;
    height: 200px;
    position: absolute;
    top: 100%;
    left: 0;
    background: rgba(255, 255, 255, 0.76);
    display: none;
}

.show .white_layer
{
    display: block;
}

.dropdown > ul
{
    padding: 0 20px;
}

.dropdown > ul > li
{
    float: left;
    margin-left: 20px;  
    text-transform: uppercase;
}

.dropdown > ul > li li
{
    text-transform: lowercase;
}

.dropdown > ul > li:first-child
{
    margin-left: 0px;    
}

.dropdown li:hover > ul
{
    display: block;
}

.dropdown > ul > li > ul ul
{
    border-left: 1px solid #888;
}

.dropdown > ul > li > a
{
    display: block;
    padding: 20px 10px;
}

.dropdown > ul > li a
{
    display: inline-block;
    padding: 10px 0;
}

.dropdown > ul ul
{
    width: 100%;
    position: absolute;
    top: 0;
    left: 100%;
    z-index: 1;
    display: none;
}

.dropdown > ul > li > ul
{
    width: 200px;
   ...

JavaScript

$(document).ready(function(){
    $('.dropdown li').hover(function(){
        if ($(this).children('ul').length > 0){    
            $('.dropdown').addClass('show');
        }
    }, function(){
        if ($('.dropdown > ul > li ul').css('display') != 'block'){ 
            $('.dropdown').removeClass('show');
        }   
    });
});