Bug 38312: Do not hide patron search form behind the fixed header

Bug 38312: Do not hide patron search form behind the fixed header

On the patron search form (/members/members-home.pl) if you open the
patron search form *from the header search*, part of the form will be
hidden behind the fixed header (the one with the select/clear, actions)

Before: https://snipboard.io/oF2gBA.jpg
After : https://snipboard.io/QqMiRH.jpg

Using z-index: 1000 as the header as 999

Signed-off-by: Phil Ringnalda <phil@chetcolibrary.org>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>