input: Write a function to search for a user-provided string in a given list of strings using case-insensitive matching. If a match is found, return "String matches". Otherwise, return "String doesn't match". If the list of strings is empty, return "No strings to search".
  
  assert search_string(["First", "Second", "Third"], "second") == "String matches"
  assert search_string(["First", "Second", "Third"], "FIFTH") == "String doesn't match"
  assert search_string([], "any") == "No strings to search"
  assert search_string(["First", "Second", "Third"], "") == "String doesn't match"
  assert search_string(["First", "Second", "Third"], "ThiRd") == "String matches"
output: def search_string(string_list, search_str):
      if not string_list:
          return "No strings to search"
      for s in string_list:
          if search_str.lower() == s.lower():
              return "String matches"
      return "String doesn't match"