Today you will learn how to enable the overlay in Drupal 7.x.
In order to apply that feature, you need to follow the steps below:
Enter Drupal admin panel (usually by adding ?q=user to the website address).
On the admin toolbar, click Modules.
In the Core section, enable the Overlay module.
Click Save Configuration.
Those are the basic steps you need to follow in order to have the functionality mentioned.
Feel free to check the detailed video tutorial below: