gh-103960: Dark mode: invert image brightness (#103983)

Doc/howto/logging.rst

@@ -418,6 +418,7 @@ The flow of log event information in loggers and handlers is illustrated in the
 following diagram.
 
 .. image:: logging_flow.png
+   :class: invert-in-dark-mode
 
 Loggers
 ^^^^^^^

Doc/library/hashlib.rst

@@ -430,6 +430,7 @@ Constructor functions also accept the following tree hashing parameters:
 
 .. figure:: hashlib-blake2-tree.png
    :alt: Explanation of tree mode parameters.
+   :class: invert-in-dark-mode
 
 See section 2.10 in `BLAKE2 specification
 <https://www.blake2.net/blake2_20130129.pdf>`_ for comprehensive review of tree

Doc/library/pathlib.rst

@@ -21,6 +21,7 @@ inherit from pure paths but also provide I/O operations.
 
 .. image:: pathlib-inheritance.png
    :align: center
+   :class: invert-in-dark-mode
 
 If you've never used this module before or just aren't sure which class is
 right for your task, :class:`Path` is most likely what you need. It instantiates