Beginning Flutter: 15 IconThemeData
IconThemeData provides properties to the icons. It must be the parent to the Icon widget. This is a example of how the property widget (IconThemeData) is different for the viewable widget (Icon) and is also different from the interactive widget (IconButton).
The data property was not working in the video because the parent widget Scaffold, was not capable to managing the size. If you use a Container widget as a parent to the IconThemeData widget, then the size property will work.