Accessibility fixes

- Add tab index order to navigation.
- Minor CSS changes.

Change-Id: I402d3cb8c1ac14bd930a5efcf472c1d249cfe00a
Signed-off-by: Michael Davis <michael.s.davis@ibm.com>
diff --git a/app/common/styles/layout/header.scss b/app/common/styles/layout/header.scss
index aaec5b4..fe06d0b 100644
--- a/app/common/styles/layout/header.scss
+++ b/app/common/styles/layout/header.scss
@@ -7,7 +7,7 @@
   top: 0;
   left: 0;
   right: 0;
-  z-index: 200;
+  z-index: 300;
 }
 
 .app__version {