const Border({BorderSide top: BorderSide.none, BorderSide right: BorderSide.none, BorderSide bottom: BorderSide.none, BorderSide left: BorderSide.none })

Creates a border.

All the sides of the border default to BorderSide.none.

Source 

const Border({
  this.top: BorderSide.none,
  this.right: BorderSide.none,
  this.bottom: BorderSide.none,
  this.left: BorderSide.none
});