JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="coolMenu">
    <li><a href="#">Lorem</a></li>
    <li><a href="#">Mauricii</a></li>
    <li>
        <a href="#">Periher</a>
        <ul class="noJS">
            <li><a href="#">Hellenico</a></li>
            <li><a href="#">Genere</a></li>
            <li><a href="#">Indulgentia</a></li>
        </ul>
    </li>
    <li><a href="#">Tyrio</a></li>
    <li><a href="#">Quicumque</a></li>
</ul>

CSS

#coolMenu,
#coolMenu ul {
    list-style: none;
}

#coolMenu {
    float: left;
}
#coolMenu > li {
    float: left;
}

#coolMenu li {
    position: relative; /* for making sub-menus positioned absolute */
}

#coolMenu li a {
    display: block;
    height: 2em;
    line-height: 2em;
    padding: 0 1.5em;
    text-decoration: none;
}
#coolMenu ul {
    display: none;
    z-index: 999;
    padding: 0;
}
#coolMenu li ul {
    position: absolute; /* place the sub-menu inside parent LI */
    top: 0; /* same top as parent's */
    left: 101px; /* this should be calculated manuallu = width of menu */
}

#coolMenu ul li a {
    width: 80px;
}
#coolMenu li:hover ul.noJS {
    display: block;
}

/* Main menu
------------------------------------------*/
#coolMenu {
    font-family: Arial;
    font-size: 12px;
    background: #2f8be8;
}
#coolMenu > li > a {
    color: #fff;
    font-weight: bold;
}

#coolMenu > li:hover > a {
    background: #f09d28;
    color: #000;
}
 
/* Submenu
------------------------------------------*/
#coolMenu ul {
    background: #f09d28;
}
#coolMenu ul li a {
    color: #000;
}
#coolMenu ul li:hover a {
    background: #ffc97c;
}

JavaScript

$('#coolMenu').find('> li').hover(function(){
    $(this).find('ul')
        .removeClass('noJS')
        .stop(true, true)
        .slideToggle('fast');
});