.leaflet-verticalcenter {
    position: absolute;
    z-index: 1000;
    pointer-events: none;
    top: 50%; /* possible because the placeholder's parent is the map */
    transform: translateY(-50%); /* using the CSS3 Transform technique */
    padding-top: 10px;
}

.leaflet-verticalcenter .leaflet-control {
    margin-bottom: 10px;
}