JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
        <li><a href="">первая</a></li>
        <li><a href="">вторая</a></li>
        <li><a href="">третья</a></li>
    </ul>

CSS

ul{
margin:0;
padding:0;
background:#000;
width:200px;
list-style:none;
}

a{
display:block;
padding:5px;
color:#fff;
font-size:14px;
text-decoration:none;
border-bottom:2px solid transparent;
}


a:hover{
border-bottom:2px solid orange;
font-size:16px;
}