Make subnavigation a bit darker color

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/framework/nav.scss

@@ -77,10 +77,10 @@
   &.sub-nav {
     text-align: center;
-    background-color: $background-color;
+    background-color: $dark-background-color;
     .container-fluid {
-      background-color: $background-color;
+      background-color: $dark-background-color;
       margin-bottom: 0;
     }

app/assets/stylesheets/framework/variables.scss

@@ -16,6 +16,7 @@ $border-color:       #e5e5e5;
 $focus-border-color:    #3aabf0;
 $table-border-color:    #f0f0f0;
 $background-color:      #fafafa;
+$dark-background-color: #f7f7f7;
 /*
  * Text
@@ -153,9 +154,6 @@ $warning-message-bg: #fbf2d9;
 $warning-message-color: #9e8e60;
 $warning-message-border: #f0e2bb;
-/* header */
-$light-grey-header: #faf9f9;
-
 /* tanuki logo colors */
 $tanuki-red: #e24329;
 $tanuki-orange: #fc6d26;