Bug 31996: Make note-style messages consistent with dialogs

Bug 31996: Make note-style messages consistent with dialogs

This patch modifies the style of divs with the class "note," making them
have the same background color as message dialogs as proposed in Bug
31973.

To test, apply the patch and rebuild the staff interface CSS.

Confirm that the updated style looks good. Some pages where you can find
examples:

- Administration -> Authorized values -> View a categories values.
- Administration -> Search engine cofiguration (with Elasticsearch
  enabled).
- Cataloging -> Batch record deletion -> Submit a list of biblionumbers.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>