How do I change the VirtualBox VM macOS High Sierra guest to full screen? When I click Full-Screen mode under the top menu bar under View it has huge black borders around the VM, while the VM is centered in the middle of the screen. I am running from a macOS High Sierra host. This is my VirtualBox version, Version 6.1.12 r139181 (Qt5.6.3). My computer is a Macbook Pro 13.3 inch.
Here is a screenshot showing the issue of the huge black border around the VM:
Does anyone know how to truly make the VM go fullscreen?