JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="nav">

    <li><a href="#" style="">Percoidei</a>
        <ul>
            <li><a href="#">Remoras</a></li>
            <li><a href="#">Tilefishes</a></li>
            <li><a href="#">Bluefishes</a></li>
            <li><a href="#">Tigerfishes</a></li>

        </ul>
    </li>

    <li><a href="#">Anabantoidei</a>
        <ul>
            <li><a href="#">Climbing perches</a></li>
            <li><a href="#">Labyrinthfishes</a></li>
            <li><a href="#">Kissing gouramis</a></li>
            <li><a href="#">Pike-heads</a></li>
            <li><a href="#">Giant gouramis</a></li>

        </ul>
    </li>

    <li><a href="#">Gobioidei</a>
        <ul>
            <li><a href="#">Burrowing gobies</a></li>
            <li><a href="#">Dartfishes</a></li>
            <li><a href="#">Eellike gobies</a></li>
            <li><a href="#">Gobies</a></li>
            <li><a href="#">Loach gobies</a></li>
            <li><a href="#">Odontobutidae</a></li>
            <li><a href="#">Sandfishes</a></li>
            <li><a href="#">Schindleriidae</a></li>
            <li><a href="#">Sleepers</a></li>
            <li><a href="#">Xenisthmidae</a></li>
        </ul>
    </li>

</ul>

CSS

#nav, #nav ul { /* all lists */
    padding: 0;
    margin: 0;
    list-style: none;
    line-height: 1;
}

#nav a {
    display: block;
    width: 10em;
}

#nav li { /* all list items */
    float: left;
}

#nav li ul { /* second-level lists */
    position: absolute;
    background: orange;
    left: -999em; /* using left instead of display to hide menus because display: none isn't read by screen readers */
}

#nav li:hover ul, #nav li.sfhover ul { /* lists nested under hovered list items */
    left: auto;
}

#content {
    clear: left;
    color: #ccc;
}