JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="main-menu">
    <li>
        <a>First List</a>
        <ul class="sub-menu">
            <li>1</li>
            <li>2</li>
            <li>3</li>
        </ul>
    </li>
    <li>
        <a>Second List</a>
        <ul class="sub-menu">
            <li>4</li>
            <li>5</li>
            <li>6</li>
        </ul>
    </li>
    <li>
        <a>Third List</a>
        <ul class="sub-menu">
            <li>7</li>
            <li>8</li>
            <li>9</li>
        </ul>
    </li>
</ul>

CSS

.main-menu{list-style:none;}
.sub-menu{display:none;}
.main-menu a:hover + .sub-menu{display:block;}