Fixes ugly layout in generated doc

Author: JohanMabille

docs/source/conf.py

@@ -9,11 +9,18 @@
 if on_rtd:
     subprocess.call('cd ..; doxygen', shell=True)
 
-import sphinx_rtd_theme
-
-html_theme = "sphinx_rtd_theme"
-
-html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
+    html_context = {
+        "css_files": [
+            "//media.readthedocs.org/css/sphinx_rtd_theme.css",
+            "//media.readthedocs.org/css/readthedocs-doc-embed.css",
+        ]
+    }
+else:
+
+    import sphinx_rtd_theme
+
+    html_theme = "sphinx_rtd_theme"
+    html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 extensions = ['breathe']
 breathe_projects = { 'xsimd': '../xml' }