.underline-animation a {
    background: linear-gradient(to right,#000000 0%,#000000 100%)!important;
    background-repeat: no-repeat!important;
    background-position: left 100%!important;
    transition-duration: 1s;
    background-size: 0 6%!important;
}

.underline-animation:hover a {
    background-size:100% 6%!important;
}