如何更改缺省标记OPENLAYERS 5

var markerStyle = new ol.style.Style({
  image: new ol.style.Icon({
    src: 'marker.png',
    size: [32, 32],
    color: '#ff0000',
    opacity: 0.8
  })
});

var markerLayer = new ol.layer.Vector({
  source: new ol.source.Vector({
    features: [
      new ol.Feature({
        geometry: new ol.geom.Point(ol.proj.fromLonLat([longitude, latitude]))
      })
    ]
  }),
  style: markerStyle
});

var map = new ol.Map({
  layers: [
    new ol.layer.Tile({
      source: new ol.source.OSM()
    }),
    markerLayer
  ],
  target: 'map',
  view: new ol.View({
    center: ol.proj.fromLonLat([longitude, latitude]),
    zoom: 10
  })
});