Fixes for focus issues on /templates page(s)

Includes:
- fixes for the cancel button, when selecting a
  template type (after clicking 'New template')
- making the folder icon black, to match the text,
  on template list items

app/assets/stylesheets/components/message.scss

@@ -147,6 +147,10 @@ $message-type-bottom-spacing: govuk-spacing(4);
       background-image: file-url('folder-blue-bold-hover.svg');
     }
 
+    &:focus {
+      background-image: file-url('folder-black-bold.svg');
+    }
+
   }
 
   &-template {

app/assets/stylesheets/components/stick-at-top-when-scrolling.scss

@@ -145,11 +145,9 @@ $sticky-padding: govuk-spacing(4);
     color: $link-hover-colour;
   }
 
-  &:focus,
-  &:active, {
-    background: $yellow;
-    color: $govuk-blue;
-    outline: none;
+  &:focus {
+    /* override default box shadow to stop it looking so large vertically */
+    box-shadow: inset 0 -4px $govuk-focus-text-colour;
   }
 
 }