When working with XAML, using a centralized Style allows you to update a set of styled views from one place. All the idiom and platform adjustements can also be integrated to your styles.
<Style TargetType="StackLayout">
  <Setter Property="Padding">
    <Setter.Value>
      <OnPlatform x:TypeArguments="Thickness" 
                  iOS="10" 
                  Android="20"/>
    </Setter.Value>
  </Setter>
</Style>