JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="menu">
    <li><a href="#">test</a></li>
</ul>

CSS

.menu li a:hover { color: #cba749; }
.menu li a {
    display: inline-block;     
    color: #858585;
    font-size: 12px;
    text-decoration: none;
    font-weight: 300;
    text-transform: uppercase;
    position: relative;
}
.menu li a:after {
    display: block;
    position: absolute;
    left: 0;
    bottom: -2px;
    width: 0;
    height: 2px;
    background-color: #cba749;
    content: "";
    transition: width 0.2s;
    -webkit-transition: width 0.2s;
    -moz-transition: width 0.2s;
    -ms-transition: width 0.2s;
    -o-transition: width 0.2s;
}
.menu li a:hover:after {
    width: 100%;
}