Stretchy Navigation Line - SS 7.0

Use this code

/* 70 stretch nav underline hover */
nav .nav-item a:after {
    content: "";
    position: absolute;
    height: 1px;
    width: 0;
    z-index: 9999;
    bottom: 0;
    left: 50%;
    transform: translateX(-50%);
    background-color: white;
    transition: all 0.3s;
}
nav .nav-item a {
    position: relative;
}
nav .nav-item a:hover:after {
    width: 100%;
    transition: all 0.3s;
}