code: def set_back(self, x: int, y: int, r: int, g: int, b: int) -> None:
          
          i = self.width * y + x
          self.back_r[i] = r
          self.back_g[i] = g
          self.back_b[i] = b
docs: Set the background color of one cell.
  
          Args:
              x (int): X position to change.
              y (int): Y position to change.
              r (int): Red background color, from 0 to 255.
              g (int): Green background color, from 0 to 255.
              b (int): Blue background color, from 0 to 255.