<li class="nav-item"><a href="/" class="nav-link">HOME</a></li>

.nav-item{
    line-height: 40px;
    position: relative;
}
.nav-item a.nav-link{
    color: #fff;
    transition: color .2s ease-out;
}
.nav-item::after{
    content: "";
    position: absolute;
    left: 0;
    top: 0;
    height: 40px;
    background: linear-gradient(to right, #e33c07, #c6020e);
    z-index: -1;
    width: 0;
}