Add a light hover effect on navbar items.

Change-Id: I3e4e42414590cf94713d9ef53123d4e8c51986ea
diff --git a/src/main/resources/META-INF/resources/cms2/base.css b/src/main/resources/META-INF/resources/cms2/base.css
index ebfeeca..088aa65 100644
--- a/src/main/resources/META-INF/resources/cms2/base.css
+++ b/src/main/resources/META-INF/resources/cms2/base.css
@@ -110,6 +110,10 @@
   padding-left: 1em;
 }
 
+body > nav a:hover {
+  background-color: #f8f8f8;
+}
+
 body > main {
   grid-area: main;