const EdgeInsets.only({double left: 0.0, double top: 0.0, double right: 0.0, double bottom: 0.0 })

Creates insets with only the given values non-zero.

Source 

const EdgeInsets.only({
  this.left: 0.0,
  this.top: 0.0,
  this.right: 0.0,
  this.bottom: 0.0
});