Variablize backdrop for modal and offcanvas

js/src/offcanvas.js

@@ -45,6 +45,7 @@ const DefaultType = {
 }
 
 const CLASS_NAME_SHOW = 'show'
+const CLASS_NAME_BACKDROP = 'offcanvas-backdrop'
 const OPEN_SELECTOR = '.offcanvas.show'
 
 const EVENT_SHOW = `show${EVENT_KEY}`
@@ -177,6 +178,7 @@ class Offcanvas extends BaseComponent {
 
   _initializeBackDrop() {
     return new Backdrop({
+      className: CLASS_NAME_BACKDROP,
       isVisible: this._config.backdrop,
       isAnimated: true,
       rootElement: this._element.parentNode,