Bug 35810: Add back to top button on staff pages

Bug 35810: Add back to top button on staff pages

Test plan:

1) Apply this patch and rebuild css with 'yarn build'
2) For example, perform a search from catalogue
3) Scroll down to see the button appear and scroll up to see it
   disappear

Note that it's works also on patron search etc..

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Emily Lamancusa <emily.lamancusa@montgomerycountymd.gov>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 926e87de86496003915247bf6d50e4290fd3a1e4)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>