By default we have 16 horizontal paddings in ExpansionTile's header, because it is ListTile and it has
/// If null, `EdgeInsets.symmetric(horizontal: 16.0)` is used.
final EdgeInsetsGeometry contentPadding;
So we have spaces on left and right
How to remove them?
The chosen answer is not working fully. In order to get it right you should go :
ListTileTheme(
contentPadding: EdgeInsets.all(0),
dense: true,
horizontalTitleGap: 0.0,
minLeadingWidth: 0,
child: ExpansionTile(...)
)