JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li><a href="#">Level 1</a>
        <ul>
            <li><a href="#">Level 2</a></li>
            <li>
                <a href="#">Level 2</a>
                <ul>
                    <li><a href="#">Level 3</a></li>
                    <li><a href="#">Level 3</a></li>
                    <li><a href="#">Level 3</a></li>
                </ul>
            </li>
            <li><a href="#">Level 2</a></li>
        </ul>
    </li>
</ul>

CSS

body {
    margin: 0;
    padding: 1em;
}
body > ul {
    border-bottom: 1px solid black;
    overflow: hidden;
}
a {
    text-decoration: none;
}
ul {
    margin: 0;
    padding: 0;
    list-style-type: none;
}
li {
    line-height: 2em;
    position: relative;
}
li ul {
    padding-left: 1em;
}
li:after {
    content:"\00A0";
    position: absolute;
    width: 200%;
    left: -100%;
    top: 0;
    border-top: 1px solid black;
    z-index: -1;
}