JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="top_menu">
     <li><a href="#">Learn</a></li>
     <li class="active"><a href="#">Market</a></li>
</ul>

CSS

.active {
    z-index: -1; 
    position: absolute;
    border-bottom: 2px solid #b6ff00;
    border-left: 1px solid transparent;
    border-right: 1px solid transparent;
}