#nav ul li h2 a:before {
    content: "";
    position: absolute;
    left: 50%;
    bottom: 0;
    width: 0;
      height: 0.02rem;
    background: #fff;
    transition: 1.2s 0.2s;
    transform: translateX(-50%);}
#nav ul li.on h2 a:before {
    width: .5rem;}