Example of Global Styles in Xamarin.Forms applications - http://julianocustodio.com/global-styles

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:DemoTimeLine"
             x:Class="Style.MainPage">
    <StackLayout HorizontalOptions="CenterAndExpand"
                 VerticalOptions="CenterAndExpand">
      
	<Label Text="Welcome to Xamarin.Forms!"
               Style="{StaticResource TitleStyle}"/>
        
        <Button Text="Save"
                Style="{StaticResource ButtonStyle}"/>
    </StackLayout>
</ContentPage>