buildings-figure-ground: use black polygons as list markers

buildings-figure-ground.json

@@ -13,7 +13,8 @@
         ]
     },
     "feature": {
-        "markerSymbol": null,
+        "markerSymbol": "",
+        "listMarkerSymbol": "{{ markerPolygon({fillColor: \"#000000\", fillOpacity: 1 })|raw }}",
         "priority": [
             "{% set p = 100 %}",
             "{% if tags.name %}{% set p = p - 10 %}{% endif %}",