Bug 21148: Dropdowns styled by the Select2 plugin do not highlight missing required...

Bug 21148: Dropdowns styled by the Select2 plugin do not highlight missing required fields

This patch adds some CSS to target mandatory fields on the add item
screen which are styled by the Select2 plugin.

To test you must have at least one item field marked mandatory and
linked to an authorized value.

Open the add item form for an existing record. Try to submit the form
without making a selection in the mandatory dropdown. You should get an
alert warning you that you have empty mandatory fields, and the field
should be highlighted in yellow.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 62aacb5865719e27224bf8f1963de1888d2ca05d)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>