Improve highlighting of some code blocks. (GH-6401)

(cherry picked from commit 46936d5a71d1683dbd8ddb6d7f39aab50ecfec50)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Doc/library/json.rst b/Doc/library/json.rst
index bcad61a..85798fa 100644
--- a/Doc/library/json.rst
+++ b/Doc/library/json.rst
@@ -100,9 +100,9 @@
     ['[2.0', ', 1.0', ']']
 
 
-.. highlight:: bash
+Using :mod:`json.tool` from the shell to validate and pretty-print:
 
-Using :mod:`json.tool` from the shell to validate and pretty-print::
+.. code-block:: shell-session
 
     $ echo '{"json":"obj"}' | python -m json.tool
     {
@@ -113,8 +113,6 @@
 
 See :ref:`json-commandline` for detailed documentation.
 
-.. highlight:: python3
-
 .. note::
 
    JSON is a subset of `YAML <http://yaml.org/>`_ 1.2.  The JSON produced by
@@ -647,8 +645,6 @@
 when serializing instances of "exotic" numerical types such as
 :class:`decimal.Decimal`.
 
-.. highlight:: bash
-
 .. _json-commandline:
 
 Command Line Interface
@@ -665,7 +661,9 @@
 and pretty-print JSON objects.
 
 If the optional ``infile`` and ``outfile`` arguments are not
-specified, :attr:`sys.stdin` and :attr:`sys.stdout` will be used respectively::
+specified, :attr:`sys.stdin` and :attr:`sys.stdout` will be used respectively:
+
+.. code-block:: shell-session
 
     $ echo '{"json": "obj"}' | python -m json.tool
     {
@@ -684,7 +682,9 @@
 
 .. cmdoption:: infile
 
-   The JSON file to be validated or pretty-printed::
+   The JSON file to be validated or pretty-printed:
+
+   .. code-block:: shell-session
 
       $ python -m json.tool mp_films.json
       [