leaflet centered label

HTML

<link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.5/leaflet.css">
<script src="http://cdn.leafletjs.com/leaflet-0.5/leaflet.js"></script>
<script src="http://leaflet.github.io/Leaflet.label/leaflet.label.js"></script>
<div id="map" style="position: absolute; top: 0; left: 0; width: 100%; height: 100%;"></div>

CSS

.leaflet-label {
    width: 100px;
    line-height: 12px;
    text-align: center;
}
.leaflet-label .pct{
font-size: 20px;
font-weight: 600;
}

JavaScript

var map = new L.Map('map', {center: new L.LatLng(-37.76525, 175.2558), zoom: 12 });

var polygon = L.multiPolygon([
    [[-37.7599, 175.2515], [-37.7599, 175.2595], [-37.7653, 175.2595], [-37.7653, 175.2515], [-37.7599, 175.2515]]]).addTo(map);

var label = new L.Label({
    offset: [-50,-7]
});
label.setContent("<span class='pct'>81%</span>");
label.setLatLng(polygon.getBounds().getCenter());
map.showLabel(label);