Update utils.js

Author: benhatsor

utils.js

@@ -35,7 +35,9 @@ const body = document.body,
       searchClear = searchScreen.querySelector('.clear'),
 
       addButton = titleScreen.querySelector('.add'),
-
+      
+      sidebarBackground = document.querySelector('.sidebar-background'),
+      
       fileWrapper = sidebar.querySelector('.files'),
 
       versionEl = learnWrapper.querySelector('.version'),