add an option to change background color

index.html

@@ -43,6 +43,10 @@
 					<th><kbd>0</kbd></th>
 					<td>Reset gamepad zoom</td>
 				</tr>
+				<tr>
+					<th><kbd>B</kbd></th>
+					<td>Change background color</td>
+				</tr>
 				<tr>
 					<th><kbd>C</kbd></th>
 					<td>Change active gamepad color</td>

js/gamepad.js

@@ -11,11 +11,15 @@ class Gamepad {
         this.gamepadDemo = new GamepadDemo(this);
 
         // cached DOM references
+        this.$body = $('body');
         this.$gamepad = $('.gamepad');
         this.$nogamepad = $('.no-gamepad');
         this.$debug = $('.debug');
         this.$help = $('.help');
 
+        this.backgroundColors = ['transparent', 'dimgrey', 'black', 'green', 'magenta'];
+        this.backgroundColorIndex = 0;
+
         // gamepad collection default values
         this.gamepads = {};
         this.gamepadIdentifiers = {
@@ -150,6 +154,9 @@ class Gamepad {
             case "Escape":
                 this.removeGamepad(true);
                 break;
+            case "KeyB":
+                this.changeBackgroundColor();
+                break;
             case "KeyC":
                 this.changeGamepadColor();
                 break;
@@ -436,6 +443,25 @@ class Gamepad {
         }
     }
 
+    /**
+     * Changes the background color
+     *
+     * @param {any} backgroundColor
+     */
+    changeBackgroundColor(backgroundColor) {
+        if ('undefined' === typeof gamepadColor) {
+            this.backgroundColorIndex++;
+            if (this.backgroundColorIndex > this.backgroundColors.length - 1) {
+                this.backgroundColorIndex = 0;
+            }
+        } else {
+            this.backgroundColorIndex = backgroundColor;
+        }
+
+
+        this.$body.css('background', this.backgroundColors[this.backgroundColorIndex]);
+    }
+
     /**
      * Changes the active gamepad color
      *
@@ -447,7 +473,6 @@ class Gamepad {
             return;
         }
 
-        const activeGamepad = this.getActiveGamepad();
         if ('undefined' === typeof gamepadColor) {
             // no color was specified, load the next one in list
             this.activeGamepadColorIndex++;