on hover underline from center

underline from center

a::after {
    position: absolute;
    left: 50%;
    right: 50%;
    height: 3px;
    bottom: -10px;
    content: "";
    background-color: #00e8bb;
    -webkit-transition: 0.5s cubic-bezier(0.68, -0.55, 0.265, 1.55);
    -o-transition: 0.5s cubic-bezier(0.68, -0.55, 0.265, 1.55);
    /* transition: 0.5s cubic-bezier(0.68, -0.55, 0.265, 1.55); */
    /* -webkit-transform: translate3d(0, 0, 0); */
    /* transform: translate3d(0, 0, 0); */}

a:hover::after {
    left: 0;
    right: 0;
}

.outer a { position: relative; }