Why darkens the screen in VirtualBox?

Set to play with CentOS 7. Freewheeling the guest additions. When you enable full screen mode, the screen darkens a little, as if the brightness has reduced, and the edges of the screen remain as light as it should. Such nonsense and with Host+F and Host+L. Where to dig?
July 8th 19 at 16:42
1 answer
July 8th 19 at 16:44
it Linux hangs , it happens
Hangs? Everything works smoothly, without brakes. Just darkens the screen and all - Titus_Kuhlman76 commented on July 8th 19 at 16:47
: I do that when Linux hangs , it happens and the browser of the same type it gets dark , then I close it and open again - you must have something else - Sasha.Gorczany commented on July 8th 19 at 16:50

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