With the seamless windows feature of
Windows guests.
Supported Linux or Oracle Solaris guests running the X Window System.
After seamless windows are enabled,
To enable seamless mode, after starting the virtual machine, press the Host key + L. The Host key is normally the right control key. This will enlarge the size of the VM's display to the size of your host screen and mask out the guest operating system's background. To disable seamless windows and go back to the normal VM display, press the Host key + L again.