input: def count_unique_case_sensitive_chars(s: str) -> int:
      """
      Given a string s, count the characters that are present in both their lowercase and uppercase forms within the string.
  
      Examples:
      >>> s = "aaAbcBC"
      3
      >>> s = "abc"
      0
      >>> s = "abBCab"
      1
  
      Constraints:
      1 <= s.length <= 50
      String s contains only lowercase and uppercase English letters.
      """
output:     lower_chars = set()
      upper_chars = set()
  
      for char in s:
          if char.islower():
              lower_chars.add(char)
          elif char.isupper():
              upper_chars.add(char)
  
      count = 0
      for char in lower_chars:
          if char.upper() in upper_chars:
              count += 1
  
      return count