Polygon layer has a white background which covers base maps

问题

I am currently creating a webmap with leaflet. I used leaflet.ajax to import polygons from a geojson. But the new polygon layer covers the basemap, resulting in the polygons on a white background.

https://virgilxw.github.io/Singapore_Election_1955/

If you go the github page and navigate to the layer menu, you can find the polygon layer under "Data".

I have tried re-ordering the layers, but moving the base map above the polygons just result in the polygons being covered.

// Default base Map
map.addLayer(layerOneMapSG_Default);

// Add geojson
var Layer1955Wards = new L.GeoJSON.AJAX("data/wards1955.geojson");

// Styled Layer Control
var baseMaps = [
    {
        groupName: "Base Maps",
        expanded: true,
        layers: {
            "OneMap": layerOneMapSG_Default
        }
    }];

var overlays = [
    {
        groupName: "data",
        expaned: "true",
        layers: {
            "Constituencies": Layer1955Wards
        }
    },
    {
        groupName: "Map Overlays",
        expanded: "true",
        layers: {
            "1953 Topological": Layer1953Topo,
            "1953 Aerial Photographs": Layer1953Aerial
        }
            }];

var styledLayerControlOptions = {
    container_width: "300px",
    container_maxHeight: "350px",
    group_maxHeight: "80px",
    exclusive: false
};

var styledLayerControl = L.Control.styledLayerControl(baseMaps, overlays, styledLayerControlOptions);
map.addControl(styledLayerControl, overlays);

来源：https://stackoverflow.com/questions/57375327/polygon-layer-has-a-white-background-which-covers-base-maps