input: Write a function to search a list of strings for any matches with an input string provided by the user. The function should return "String matches" if any match is found, otherwise it should return "String doesn't match". The function should handle any case sensitivity issues by converting all input strings to the same case.
  
  assert search_strings(["First", "Second", "Third"], "first")=="String matches"
  assert search_strings(["First", "Second", "Third"], "FIRST")=="String matches"
  assert search_strings(["First", "Second", "Third"], "FOURTH")=="String doesn't match"
  assert search_strings(["First", "Second", "Third"], "cond")=="String doesn't match"
  assert search_strings([], "any")=="String doesn't match"
output: def search_strings(string_list, input_string):
      input_string = input_string.lower()
      for s in string_list:
          if s.lower() == input_string:
              return "String matches"
      return "String doesn't match"