input: Write a python function to get element details by its name.
  assert get_element_details("Hydrogen") == {"symbol": "H", "atomic_number": 1, "atomic_mass": 1.008, "group": 1, "period": 1}
  assert get_element_details("Helium") == {"symbol": "He", "atomic_number": 2, "atomic_mass": 4.003, "group": 18, "period": 1}
  assert get_element_details("Oxygen") == None
output: def get_element_details(element_name):
      elements = {
          "Hydrogen": {"symbol": "H", "atomic_number": 1, "atomic_mass": 1.008, "group": 1, "period": 1},
          "Helium": {"symbol": "He", "atomic_number": 2, "atomic_mass": 4.003, "group": 18, "period": 1}
      }
      return elements.get(element_name)