input: Write a function to generate a Python program that takes two lists as input and returns a new list containing only the common elements. If there are no common elements, return an empty list.
  assert common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10]) == [2, 8]
  assert common_elements([1, 2, 3, 4], [5, 6, 7, 8]) == []
  assert common_elements([], [5, 6, 7, 8]) == []
  assert common_elements([1, 2, 3, 4, 5], [5, 4, 3, 2, 1]) == [1, 2, 3, 4, 5]
output: def common_elements(list1, list2):
      return list(set(list1) & set(list2))