Be more flexible on how the stylesheet is added

dev-docs/source/conf.py

@@ -11,17 +11,15 @@ from distutils.version import LooseVersion
 
 
 # -- General configuration ------------------------------------------------
-
 if LooseVersion(sphinx_version) > LooseVersion("1.6"):
+
     def setup(app):
         """Called automatically by Sphinx when starting the build process
         """
-        # Add support for multiple Sphinx versions
-        if hasattr(app, "add_css_file"):
+        if hasattr(app, 'add_css_file'):  # >=v1.8
             app.add_css_file("custom.css")
         else:
-            app.add_stylesheet("custom.css")
-
+            app.add_stylesheet("custom.css")  # v1.6-1.8
 
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom