When my sketch, which has a black background, runs on the web on a page also with a black background, there is a grey fine-dotted border around the sketch window.

I would very much like to get rid of it -- I've checked the ref., three books, and can't find anything about this mysterious border.

The interesting thing is, that when the sketch/page first loads, there is no border. Thereafter it appears with each mouse click----which tells me that the issue is in my code -- but I am unable to find it.

I have changed all sorts of things which might be related to a border, but nothing changes.

1. ////////////////////////////////////////////
   // Clair Dunn 15SEP2013 CHAOS OUT OF ORDER
   ////////////////////////////////////////////
   int i;
   void draw() {
   //  stroke(0); //tried this to see if border vanished - didn't
   };
   void setup()
   {
     size (500, 500);
     background(0);
     for (int i=0; i<100; i++)
     {
       drawRectangle(random(width), random(height), random(200), random(200));
     }
   }
   
   void drawRectangle(float x, float y, float w, float h)
   {
     if (x+width/2 >=499)
     {
       fill(random(255), random(255), random(255));
       stroke(0);
       strokeWeight(2);
       triangle (x-200, int (random(400)), 100, 100, 35, int(random(150)));
     }
     else
     {
       int opacity = int (random(255));
       noStroke();
       fill(random(255), random(255), random(255), opacity);
       rect( x, y, w, h);
     }
   }
   void mousePressed()
   {
   //  background(random(255), random(255), random(255));
     background(0);
     for (int i=0; i<100; i++)
     {
       noStroke(); 
       drawRectangle(random(width), random(height), random(200), random(200));
     }
   }

You can't see the border when you just run it in the processing window, but you can see it on the web if you need to.

http://www.clairdunn.com/chaos-out-of-order.htm

Thanks much for any ideas!