Change look and feel of the `ansible-core` docs (#74200) (#74482)

* Change look and feel of the `ansible-core` docs (#74200)

(cherry picked from commit d7f826c987)

* lighten navigation background to make section labels easier to read for core docs (#74356)

* make section labels for /ansible-core/ docs easier to read, with black text and lighter gray background

(cherry picked from commit 6119fb0a9a)

Co-authored-by: Sandra McCann <samccann@redhat.com>

docs/docsite/sphinx_conf/core_conf.py

@@ -169,7 +169,7 @@ html_context = {
     'latest_version': '2.10',
     # list specifically out of order to make latest work
     'available_versions': ('2.10', 'devel',),
-    'css_files': ('_static/ansible.css',  # overrides to the standard theme
+    'css_files': ('_static/core.css',  # overrides to the standard theme
                   ),
 }