App Builder User's Guide Using Themes and Theme Styles 12 Using Themes and Theme Styles Developers can alter a database application's user interface and page layout through themes and templates. Using ThemesUse themes and theme styles to increase your productivity when building an application. Managing Themes and SubscriptionsDevelopers can manage themes directly or through the use of theme subscriptions. Creating Custom ThemesCreate a custom theme by modifying an existing templates. Using Custom Cascading Style SheetsUpload or reference a cascading style sheet.