Full Screen in Ubuntu

Recently, after VirtualBox is installed, it is found that after Ctrl + F is used to enter the full screen, gnome-panle is always taken to the full screen, making it inconvenient to use windows.
Later, it was found that the VirtualBox window was not set when it was not full screen (that is, in Ubuntu), and the tool bar under the VM could not be seen. If you enter full screen, the task bar under gnome will be followed into full screen.
Therefore, if you can adjust the VirtualBox window, the adjustment to the VirutalBox window is not maximized, and you can see the bottom toolbar on the screen, then entering the full screen will be OK.
If you cannot adjust VirtualBox like me, the reason is that I have entered the 1024*768 resolution, and VirutalBox is full of the whole screen, as a result, I cannot adjust the VirtualBox window to display the toolbar. In this way, you can first set the resolution to 800*600 in the virtual machine, and then the VirtualBox will become smaller, press Ctrl + F to enter the full screen. Do you find that there is no gnome toolbar in 800*600? haha. Now we can adjust the Virtual Machine resolution to 1024*768. Well, there are still no gnome tool bars. After the problem is solved, you exit the full screen mode and the VirtualBox window also changes. Now you can see the VirtualBox toolbar on the screen and then enter the full screen.