The App Builder canvas
The App Builder canvas is that part of the workspace in which you actually
construct your project/app. It can be divided into multiple Flexboxes and have multiple sets
of boundaries.
You construct App Builder projects/apps by selecting components and then placing them within the Flexboxes that have been defined for the project.
To make it possible for your app to adapt to different devices (for example, laptops and mobile phones), you make boundary settings that the app then responds to automatically to display the correct layout for each device.