JSFiddle - React, Tailwind, and code Playground

HTML

<nav> <a href="#">Menü</a>

    <ul>
        <li><a href="#">Startseite</a>

        </li>
        <li><a href="#">Moderator</a>

        </li>
        <li><a href="#">Archiv</a>

        </li>
        <li><a href="#">Impressum</a>

        </li>
    </ul>
</nav>

CSS

nav > ul {
    display: none;
    list-style: none;
    margin: 0;
    padding: 0;
}
nav a {
    background: #efefef;
    color: #000;
    cursor: pointer;
    display: block;
    margin-bottom: 1px;
    padding: 1em;
    text-decoration: none;
}
nav a:active, nav a:hover {
    background: #999;
}
nav > a:after {
    content:" öffnen";
}
nav > a:focus {
    display: none;
}
nav > a:focus ~ ul {
    display: block;
}