Cross.fromList constructor
Construct cross from an existing 6x6 matrix.
Cross.fromList(this.grid); is a constructor in the Cross class that takes
a 2D list grid as a parameter. It creates a new instance of the Cross
class by assigning the grid parameter to the grid property of the new
instance. This allows you to create a Cross object from an existing 2D list.
Implementation
Cross.fromList(this.grid);