JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main_menu">
    <ul class="menu">
        <li><a>Home</a></li>
        <li><a>Whatever</a></li>
        <li class="whatever">
            <a>Products</a>
            <ul class="sub-menu">
                <li><a>What When How</a></li>
                <li><a>Who Why</a></li>
            </ul>
        </li>
        <li><a>Contacts</a></li>
    </ul>
</div>

<div id="contents"></div>

CSS

#main_menu .menu {
    list-style: none outside none;
    text-align: center;
    text-transform: uppercase;
    height:50px;
}

#main_menu li {
    display: inline-block;
    list-style: none outside none;
    cursor:pointer;
}

#main_menu .menu li a:hover, #main_menu .menu li:hover > a {
    background-color: #4A6125;
    color: white;
    text-decoration: underline;
}

#main_menu .menu ul {
    margin: 0 auto;
    position: relative;
    text-align: center;
}

#main_menu .sub-menu {
    background-color: #000000;
    color: #FFFFFF;
    list-style: none outside none;
    text-transform: uppercase;
}

#main_menu ul ul {
    display: none;
    float:left;
    left: 0;
    margin: 0;
    position: absolute;
    width: 150px;
    z-index: 999999;
}

#main_menu a {
    color: black;
    display: block;
    font-size: 12px;
    height: 13px;
    padding: 24px 20px 15px;
    text-align: center;
    text-decoration: none;
}

#main_menu .menu .sub-menu li a {
    background-color: #000000;
    color: #FFFFFF;
    padding: 10px;
}

#contents {
    float:left;
    background:gold;
    width:100%;
    height:200px;
}

JavaScript

$(".whatever").hover(function() {
    $("#main_menu ul ul ").css("display", "block ")
}, function() {
    $("#main_menu ul ul ").css("display", "none ")
})