Theme are different between different user I grant permission of menu ['node/add'] to a certain role of users (which was only accessible by admin previously). Turns out that, these two types of users have different views of this menu (As you can see from the following two screen shots). 

How can I theme the page for these two users in the same way? Or How can I change the theme for the non admin user?

-----------update-----------

If I don't want to use admin theme, where should I add my own theme?
Go to /admin/people/permissions
Enable the "View the administration theme" permission for the appropriate role.
Save the form.


Users with that role will now see the admin theme (as set at /admin/appearance) wherever applicable.