input: Write a function to find the maximum element in a list.
  assert find_max_element([1, 10, 50, 3, 8]) == 50
  assert find_max_element([5, 2, 9, 1, 6]) == 9
  assert find_max_element([100, 200, 50, 300, 250]) == 300
output: def find_max_element(lst):
      if not lst:
          return None
      max_element = lst[0]
      for element in lst:
          if element > max_element:
              max_element = element
      return max_element