use rtd theme

conf.py

@@ -112,7 +112,14 @@
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-html_theme = 'alabaster'
+# html_theme = 'default'
+
+# on_rtd is whether we are on readthedocs.org
+on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
+if not on_rtd:  # only import and set the theme if we're building docs locally
+    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