input: Write a function to find the closest pair of numbers between two lists.
  assert closest_pair([1, 3, 15, 11, 2], [23, 127, 235, 19, 8]) == (11, 8)
  assert closest_pair([10, 5, 40], [50, 90, 80]) == (40, 50)
  assert closest_pair([1, 5, 9], [20, 35, 17]) == (9, 17)
output: def closest_pair(list1, list2):
      list1.sort()
      list2.sort()
      i, j = 0, 0
      min_diff = float('inf')
      pair = (None, None)
  
      while i < len(list1) and j < len(list2):
          diff = abs(list1[i] - list2[j])
          if diff < min_diff:
              min_diff = diff
              pair = (list1[i], list2[j])
          
          if list1[i] < list2[j]:
              i += 1
          else:
              j += 1
      
      return pair