Improvements

- Add .contrast variant
- Separate _button-styles.scss
- Edit .secondary, mark, figcaption, hgroup, tooltips
- Docs: Add More about grids, External links icon, Second theme switcher

scss/components/_nav.scss

@@ -48,6 +48,12 @@ nav {
     &:focus {
       text-decoration: none;
     }
+
+    @if $enable-classes {
+      &.contrast:not([role="button"]) {
+        box-shadow: none;
+      }
+    }
   }
 }