<style>

:any-link {
    position: relative;
    color: hsl(200, 100%, 40%);
    text-decoration: none;
}

:any-link::after {
    position: absolute;
    right: -0.05em;
    bottom: 0.05em;
    left: -0.05em;
    content: "";
    border-bottom: 0.1em solid;
    transition: transform 100ms ease-out;
}

:any-link:not(:hover)::after {
    transform: rotateY(90deg);
}

</style>

<a href="#">Hello World!</a>