Fix up ReadTheDocs documentation builds.

.readthedocs.yaml

@@ -17,6 +17,6 @@ sphinx:
 
 # We recommend specifying your dependencies to enable reproducible builds:
 # https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
-# python:
-#   install:
-#   - requirements: docs/requirements.txt
+python:
+  install:
+  - requirements: docs/requirements.txt

docs/conf.py

@@ -106,13 +106,9 @@ def _version_info():
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 
-on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
-if on_rtd:
-    html_theme = 'default'
-else:
-    import sphinx_rtd_theme
-    html_theme = 'sphinx_rtd_theme'
-    html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
+import sphinx_rtd_theme
+html_theme = 'sphinx_rtd_theme'
+html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the

docs/requirements.txt

@@ -0,0 +1,2 @@
+sphinx
+sphinx_rtd_theme