Buttons initiate app-specific actions when tapped, have customizable backgrounds, and can include a title or an icon. Although iOS provides a number of predefined button styles, CarPlay supports only the system button style.
System buttons often appear in navigation bars, but may be used anywhere.
Use verbs in titles. An action-specific title, such as Add Favorite, shows that a button is interactive and says what happens when you tap it.
Use title-case for titles. Capitalize every word except articles, coordinating conjunctions, and prepositions of four or fewer letters.
Keep titles short. Overly long text can crowd your interface and may get truncated on smaller screens.
Consider adding a border or a background only when necessary. By default, a button has no border or background. In some content areas, however, a border or background is necessary to denote interactivity. In the Phone app, bordered number keys reinforce the traditional model of making a call, and the background of the Call button provides an eye-catching target that’s easy to hit.