section h2 {
    text-align: center;
}

section h2::after {
    content: "";
    display: block;
    max-width: 250px;
    margin: 25px auto 30px;
    border-top: solid 5px #000;
}

nav + section {
    margin-top: 50px;
}

@media (min-width: 768px) {
    nav + section {
        margin-top: 100px;
    }
}