Hello! I recently installed Sierra 10.12 in VirtualBox and didn't allocate enough disk space for it. Now I'm trying to expand disk partition with Gparted utility: I created new VM that is of type Mac OS X, mounted iso Gparted file to IDE controller and vdi file of my macOS to SATA controller. After that I started it and got Gparted window. When I choose to expand some partition (I have 3:dev/sda1(EFI), dev/sda2(VirtualBoxDisk (my macOS partition, that I intend to increase)) and dev/sda3(Recovery HD)), right to that there's some unallocated space, the slider doesn't move to the right and I cannot set amount of new space to this partition more than already set in the box.
What should I do to expand my partition? Thanks in advance.