JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
    <div id="button">
        <p>Drop Down</p>
    </div>
    <div id="dropdown">
        <ul id="content">
            <li><a href="#">Text</a>
            </li>
            <li><a href="#">Text</a>
            </li>
            <li><a href="#">Text</a>
            </li>
            <li><a href="#">Text</a>
            </li>
            <li><a href="#">Text</a>
            </li>
        </ul>
    </div>
</div>

CSS

body {
    font-family: Raleway, 'Helvetica Neue', Helvetica, sans-serif;
}
.wrapper {
    margin: 0 auto;
    width: 200px;
}
#button {
    position: relative;
    top: 10px;
    left: 0;
    width: 150px;
    height: 35px;
    margin: 0;
    padding: 0px 5px 2px 5px;
    border-radius: 5px;
    background: #393939;
    cursor: pointer;
}
#button p {
    text-align: center;
    font-size: 14px;
    font-weight: 100;
    letter-spacing: 2px;
    line-height: 38px;
    color: #fff;
}
#dropdown {
    position: relative;
    top: 7px;
    left: 0;
    width: 150px;
    height: 0px;
    margin: 0;
    padding: 0px 5px 2px 5px;
    border-radius: 0px 0px 5px 5px;
    background: #393939;
    transition: 0.5s;
    cursor: pointer;
    overflow: hidden;
}
#content {
    list-style: none;
    margin: 0;
    padding: 5px 0 0 5px;
    opacity: 0;
}
#content li {
    margin: 0 0 10px 0;
    padding: 0;
}
#content li a {
    text-decoration: none;
    margin: 0;
    padding: 0;
    font-weight: 100;
    letter-spacing: 2px;
    color: #fff;
}

JavaScript

(function () {
    "use strict";

    var dropdown = document.getElementById('dropdown'),
        content = document.getElementById('content'),
        button = document.getElementById('button');

    button.onclick = function () {

        if (dropdown.style.height === "150px") {
            dropdown.style.height = "0";
            content.style.opacity = "0";

        } else {
            dropdown.style.height = "150px";
            dropdown.style.transition = "height 0.5s";
            content.style.transition = "opacity 0.5s";
            content.style.opacity = "1";
        }

    };
})();