The shared control for creating the rounded corners

ContentViewRoundedCorners.cs

public class ContentViewRoundedCorners : ContentView
{
    public static readonly BindableProperty CornerRaidusProperty =
        BindableProperty.Create<ContentViewRoundedCorners, float>(x => x.CornerRadius, 0);

    public float CornerRadius
    {
        get { return (float) GetValue(CornerRaidusProperty); }
        set { SetValue(CornerRaidusProperty, value); }
    }
}