Add styles needed by keyboard nav plugin changes

We'll see if these can be provided by the plugin in future.

Author: microbit-matt-hillsdon

theme/blockly-core.less

@@ -289,6 +289,19 @@ text.blocklyCheckbox {
     }
 }
 
+/* Keyboard navigation plugin styles */
+
+.passiveBlockFocus.blocklyPath {
+    stroke-dasharray: 5 3;
+    stroke-width: 3;
+    stroke: #ffa200;
+}
+
+.passiveNextIndicator {
+   stroke: #ffa200;
+   fill: #ffa200;
+ }
+
 /*******************************
         Scrollbars
 *******************************/