When you introduce Compose in an existing app, you need to migrate your themes in XML to use MaterialTheme for Compose screens. This means your app's theming will have two sources of truth: the View-based theme and the Compose theme. Any changes to your styling need to be made in multiple places. Once your app is fully migrated to Compose, you can remove your XML theming.
To migrate your XML themes to Compose, use the Material Theme Builder to migrate from an XML theme to Material 3 in Compose. You can use your existing color roles, such as primary and secondary colors from your XML theme, and pass them to the Material Theme Builder. This creates a fully Material 3 theme in Compose and provides downloadable color and theme files to use in your app.
Material Theme Builder generates a MaterialTheme and light and dark color schemes for your app. If your app uses custom shapes or typography, migrate your custom shapes and typography by defining a Shape and Typography, respectively. Once defined, provide that information to your MaterialTheme. See shapes and typography to learn more.