Alt-Tab not working for guest operating systems in Virtualbox on Fedora 25

I do lots of research on net but I couldn't find any solution to my problem. My host machine is Fedora 25 and I have two guest OS (Kali Linux and Windows 10). Both in my guest OSs every shortcut works properly(Ctrl+C etc.). But alt+tab and Windows key shortcuts doesn't work for guest os. Even i activate or deactivate host key (Right Ctrl) it still tabs between programs in host os. Please help me?