JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#">a <span>span</span></a>

CSS

a {
    background:gray;
    display:block;
    margin:100px;
    padding:100px;
}

a span {
    opacity:0;
    -webkit-transition:0.5s;
    visibility:hidden;
}

a:hover span {
    opacity:1;
    -webkit-transition:0.5s;
    visibility:visible;
}