Header is the top part of an app, generally containing the app title and a main action. It is generally declared first in Main, and only once.childrenReact nodeHeader. Overrides both primary and secondary and their default styling. You should generally prefer using primary and secondary, when possible.primaryReact nodeHeader (for left-to-right languages). It is generally where the title of an app is set.secondaryReact nodeHeader (for left-to-right languages). It is generally where the main action of an app is set.Button is used here, containing both a label and an icon, it will automatically adapt its display to the available width, displaying either the label or the icon. To override this behavior, set the display prop of the Button to something else than auto.