Render main entrances at z>=18, others at z>=19.

Also adjust marker sizes.

buildings.mss

@@ -46,20 +46,31 @@
 }
 
 #entrances {
-  ["entrance" = "yes"],
-  ["entrance" = "main"],
-  ["entrance" = "home"],
-  ["entrance" = "service"],
-  ["entrance" = "staircase"] {
+  [zoom >= 18]["entrance" != null]  {
     marker-fill: @entrance-normal;
     marker-allow-overlap: true;
     marker-ignore-placement: true;
     marker-file: url('symbols/rect.svg');
+    marker-width: 5.0;
+    marker-height: 5.0;
+    marker-opacity: 0.0;
     ["entrance" = "main"] {
+      marker-opacity: 1.0;
       marker-file: url('symbols/square.svg');
     }
-    ["entrance" = "service"] {
-      marker-file: url('symbols/corners.svg');
+  }
+  [zoom >= 19] {
+    ["entrance" = "yes"],
+    ["entrance" = "main"],
+    ["entrance" = "home"],
+    ["entrance" = "service"],
+    ["entrance" = "staircase"] {
+      marker-opacity: 1.0;
+      marker-width: 6.0;
+      marker-height: 6.0;
+      ["entrance" = "service"] {
+        marker-file: url('symbols/corners.svg');
+      }
     }
     ["access" = "yes"],
     ["access" = "permissive"] {
@@ -69,21 +80,9 @@
       marker-fill: @entrance-normal;
       marker-file: url('symbols/rectdiag.svg');
     }
-    [zoom >= 17] {
-      marker-width: 4.0;
-      marker-height: 4.0;
-    }
-    [zoom >= 18] {
-      marker-width: 6;
-      marker-height: 6;
-    }
-    [zoom >= 19] {
-      marker-width: 8.0;
-      marker-height: 8.0;
-    }
-    [zoom >= 20] {
-      marker-width: 10;
-      marker-height: 10;
-    }
+  }
+  [zoom >= 20]["entrance" != null] {
+    marker-width: 8.0;
+    marker-height: 8.0;
   }
 }

project.mml

@@ -1085,7 +1085,7 @@ Layer:
             OR tags->'indoor' IS NULL)
         AS entrances
     properties:
-      minzoom: 17
+      minzoom: 18
   - id: aeroways
     geometry: linestring
     <<: *extents