App.xaml

<?xml version="1.0" encoding="utf-8"?>
<Application xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             x:Class="FontSample.App">
	<Application.Resources>
		<ResourceDictionary>
             <Style TargetType="NavigationPage">
                <Setter Property="BackgroundColor" Value="White" />
                <Setter Property="BarBackgroundColor" Value="#08adcf" />
            </Style>
            <Style TargetType="Label">
                <Setter Property="FontFamily" Value="orangejuice" />
                <Setter Property="FontSize" Value="16" />
                <Setter Property="TextColor" Value="Black" />
            </Style>
            <Style TargetType="Button">
                <Setter Property="FontFamily" Value="orangejuice" />
                <Setter Property="FontSize" Value="16" />
                 <Setter Property="TextColor" Value="White" />
                <Setter Property="BackgroundColor" Value="Black" />
            </Style>
            <Style TargetType="Entry">
                <Setter Property="FontFamily" Value="orangejuice" />
                <Setter Property="FontSize" Value="16" />
            </Style>
            <Style TargetType="StackLayout">
                <Setter Property="Padding" Value="20" />
            </Style>
        </ResourceDictionary>
	</Application.Resources>
</Application>