[HELP] Virtualbox Video memory doesn't match Mac Graphics info

Hi, I'm new to hackintoshing,

I have successfully installed macOS High Sierra in VirtualBox, but I noticed that opening safari or chrome will result in the whole browser flickering randomly. Firefox is better, but a gray box follows my mouse around. Opening folders from dock also lags a lot.

I suspect that the video memory was not enough for my setup, so I gave the vm 256 mb of video memory. However, under "About this mac", the graphics displays only 4mb.

Is this a bug with virtualbox? Or how can I fix it?

Any help would be appreciated.

Thanks a lot!