JSFiddle - React, Tailwind, and code Playground

HTML

<a href="" class="open-menu">Toggle menu</a>

<nav class="menu">
    <ul>
        <li>Home</li>
        <li>Motivation</li>
        <li>Books</li>
        <li>Videos</li>
    </ul>
</nav>

<p>
    To facilitate the process, AI Lab hackers had built a system that displayed both the "source" and "display" modes on a split screen. Despite this innovative hack, switching from mode to mode was still a nuisance.
</p>

CSS

.menu {
    visibility: hidden;   
}

.menu.opened {
    visibility: visible;
}

JavaScript

var openMenuBtn = document.getElementsByClassName('open-menu')[0],
    menu        = document.getElementsByClassName('menu')[0];

openMenuBtn.addEventListener('click', function ( e ) {
    e.preventDefault();
    menu.classList.toggle('opened');
}, false);