Bug 21470: Due date no longer shown in red when viewing checkouts for a patron

Bug 21470: Due date no longer shown in red when viewing checkouts for a patron

This patch corrects an error in the staff client CSS which was causing
overdue items on the checkout screen to not be highlighted.

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 out to a patron who has overdues. The overdue items should have
due dates styled bold and red.

Signed-off-by: Pierre-Marc Thibault <pierre-marc.thibault@inLibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>