<Style x:Key="buttonStyle" TargetType="Button"> <Setter Property="FontSize"> <OnPlatform x:TypeArguments="x:Double"> <On Platform="Android">40</On> <On Platform="iOS">10</On> </OnPlatform> </Setter> </Style>
<OnPlatform x:Key="MyFontSize" x:TypeArguments="x:Double" iOS="14" Android="14" WinPhone="14" />