override normal flowchart arrowhead to allow css styling

src/less/dark/flow.less

@@ -9,6 +9,11 @@
   stroke-width: 1px;
 }
 
+
+.arrowheadPath {
+  fill: @arrowheadColor;
+}
+
 .edgePath .path {
   stroke: @lineColor;
 }

src/less/dark/variables.less

@@ -5,6 +5,7 @@
 @lineColor: @mainContrastColor;
 @border1: #81B1DB;
 @border2: rgba(255, 255, 255, 0.25);
+@arrowheadColor: @mainContrastColor;
 
 
 /* Flowchart variables */

src/less/default/flow.less

@@ -9,6 +9,10 @@
   stroke-width: 1px;
 }
 
+.arrowheadPath {
+  fill: @arrowheadColor;
+}
+
 .edgePath .path {
   stroke: @lineColor;
 }

src/less/default/variables.less

@@ -3,6 +3,7 @@
 @lineColor: #333333;
 @border1:#CCCCFF;
 @border2:#aaaa33;
+@arrowheadColor: #333333;
 
 /* Flowchart variables */
 @nodeBkg:@mainBkg;

src/less/forest/flow.less

@@ -12,6 +12,10 @@ color:#333
   stroke-width: 1px;
 }
 
+.arrowheadPath {
+  fill: @arrowheadColor;
+}
+
 .edgePath .path {
   stroke: @lineColor;
   stroke-width: 1.5px;

src/less/forest/variables.less

@@ -4,6 +4,7 @@
 @lineColor: green;
 @border1: #13540c;
 @border2: #6eaa49;
+@arrowheadColor: green;
 
 /* Flowchart variables */
 @nodeBkg:@mainBkg;