Create a custom animation to fade-out view in forms

Hey, sorry if this was asked before, i couldn't find any threads wich could help me.

I want to animate an element like this. It should set the opacity to 0, but not for the whole view. Instead i want the view going transparent from the center to the edge. I am using Xamarin Forms 3.4.0.1008975 and am developing for iOS and Android.

Can somebody help me with that?
Thanks