The easiest way to use Material Theme is to configure your app to use a built-in theme without
customization. If you don't want to explicitly configure a theme, your app will default to
Theme.Material (the dark theme). If your app has only one activity, you can configure a
theme at the application level. If your app has multiple activities, you can configure a theme at
the application level so that it uses the same theme across all activities, or you can assign
different themes to different activities. The following sections explain how to configure themes at
the app level and at the activity level