change bootstrap theme for spacelab

source/conf.py

diff --git a/source/conf.py b/source/conf.py
index 88660db..1754468 100644
--- a/source/conf.py
+++ b/source/conf.py
@@ -144,7 +144,7 @@
 
     # HTML navbar class (Default: "navbar") to attach to <div> element.
     # For black navbar, do "navbar navbar-inverse"
-    'navbar_class': "navbar",
+    'navbar_class': "navbar navbar-inverse",
 
     # Fix navigation bar to top of page?
     # Values: "true" (default) or "false"
@@ -176,7 +176,7 @@
     # * superhero
     # * united
     # * yeti (v3 only)
-    'bootswatch_theme': "flatly",
+    'bootswatch_theme': "spacelab",
 
     # Choose Bootstrap version.
     # Values: "3" (default) or "2" (in quotes)