Bug 32014: Tweak style of checkout settings panel

Bug 32014: Tweak style of checkout settings panel

This patch makes some minor changes to the CSS controlling the way the
checkout settings panel displays, as well as the panel showing the last
checked-out item.

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

- Go to Circulation and locate a patron to check out to.
- On the checkout page, click the "settings" icon in the barcode field.
- The checkout settings panel should display. Confirm that the spacing
  looks good.
- Check out an item to the patron.
- Confirm that the panel showing the last checked out item information
  looks correct: A green-bordered box with a white background, no
  rounded corners.

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