Merge branch 'pr/433'

src/js/plugin/default-setting.js

@@ -13,5 +13,6 @@ module.exports = {
   useKeyboard: true,
   useSelectionScroll: false,
   wheelPropagation: false,
-  wheelSpeed: 1
+  wheelSpeed: 1,
+  theme: 'default'
 };

src/js/plugin/initialize.js

@@ -23,6 +23,7 @@ module.exports = function (element, userSettings) {
   var i = instances.add(element);
 
   i.settings = h.extend(i.settings, userSettings);
+  cls.add(element, 'ps-theme-' + i.settings.theme);
 
   clickRailHandler(element);
   dragScrollbarHandler(element);