details.navbar-dropdown {
    position: relative;
}

details.navbar-dropdown > summary {
    padding: .5rem;
}

details.navbar-dropdown summary::marker {
    content: "";
    display: none;
}

details.navbar-dropdown > ul {
    position: absolute;
    margin: 0 auto;
    padding: .5rem;
    background: white;
    border: 1px solid darkgrey;
    border-radius: 3px;
    text-align: center;
}