Final answer:
The three main screen elements of the Now Platform User Interface are the Banner frame, Content frame, and Application Navigator, which include global navigation and display components.
Step-by-step explanation:
The three main screen elements of the Now Platform User Interface are the Banner frame, the Content frame, and the Application Navigator. The Banner frame typically contains logos, global search, and profile menu. The Content frame displays the main content such as lists, forms, and homepages. The Application Navigator is the menu located on the left side of the screen that allows users to switch between applications and modules within the Now Platform.