use extra_css_files option for custom css

conf.py

@@ -93,6 +93,7 @@
     "display_github": True,
     "last_updated": True,
     "commit": False,
+    "extra_css_files" : ['_static/css/gauge.css']
 }
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
@@ -101,8 +102,6 @@
 
 html_favicon = "favicon.ico"
 
-html_style = 'css/gauge.css'
-
 # -- Options for HTMLHelp output ------------------------------------------
 
 # Output file base name for HTML help builder.