This property only applies to linear gradients.
This property defines the angle the gradient path makes with the horizontal plane.
For example, a gradient which extends from left to right can be changed to extend from bottom to top by setting this property to 90 degrees.
A value of 45 degrees yields a gradient which extends from the bottom left corner of the containing element to the top right corner.
Target Platforms: Android 4.4+, iOS 8+
Development Environments: Visual Studio 2015+, Visual Studio for Mac Preview, Xamarin for Visual Studio 4.2+