Bug 25176: Fix style of checkout form

Bug 25176: Fix style of checkout form

This patch makes a small CSS change in order to fix a display problem
with the checkout form where the form's width doesn't match that of the
"last checked out" message.

To test, apply the patch and regenerate the staff client CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

Check an item out to a patron. Confirm that the green-bordered "Checked
out" message under the checkout form matches the width of the form.

Signed-off-by: David Roberts <david@koha-ptfs.co.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>