JSFiddle - React, Tailwind, and code Playground

HTML

<a class="active" href="#">EN</a><a href="#">FR</a>

CSS

a{
  display:inline-block;
  background:#fff;
  border:1px solid #ccc;
  box-sizing:border-box;
  width:3rem;
  height:3rem;
  line-height:3;
  text-align:center;
}

a.active{
  border:0;
  background:orange;
}