You can define a style inline in the XAML for a control, or as a reusable resource. Define resources in an individual page's XAML file, in the App.xaml file, or in a separate resource dictionary XAML file. A resource dictionary XAML file can be shared across apps, and more than one resource dictionary can be merged in a single app. Where the resource is defined determines the scope in which it can be used. Page-level resources are available only in the page where they are defined. If resources with the same key are defined in both App.xaml and in a page, the resource in the page overrides the resource in App.xaml. If a resource is defined in a separate resource dictionary file, it's scope is determined by where the resource dictionary is referenced.