JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <div class="submenu">
        <ul>
            <li>One</li>
        </ul>
    </div>
    <div class="submenu">
        <ul>
            <li>Two</li>
        </ul>
    </div>
</ul>
<h1>Page Title</h1>

JavaScript

document.onclick = closeMenu;

function parentIsSubmenu(child) {
     var node = child.parentNode;
     while (node != null) {
         if ((node.className || '').indexOf('submenu') > -1) {
             return true;
         }
         node = node.parentNode;
     }
     return false;
}

function closeMenu(event) {
    if(!parentIsSubmenu(event.target)) {
        var submenus = document.getElementsByClassName("submenu");
        for(var i = 0; i < submenus.length; i++) {
            submenus[i].style.display = 'none';
        }
    }
}