Tweak button margin in stacked bar chart example.

examples/stream/stack.html

@@ -28,8 +28,8 @@ button {
   text-shadow: 0 -1px 1px #222;
   padding: 6px 10px 6px 10px;
   border: 0;
+  margin: 0 0 4px 2px;
   border-bottom: 1px solid #222;
-  margin: 0 0 0 2px;
   -moz-border-radius: 5px;
   -moz-box-shadow: 0 1px 3px #999;
   -webkit-border-radius: 5px;