如何删除地图上标记上的阴影？

<div id="map" style="width: 100%; height: 400px;"></div>

function initMap() {
  var map = new google.maps.Map(document.getElementById('map'), {
    center: {lat: 40.730610, lng: -73.935242},
    zoom: 12,
    styles: [
      {
        "elementType": "labels",
        "stylers": [
          {
            "visibility": "off"
          }
        ]
      }
    ]
  });
}