Bug 19865: Add back horizontal scroll bar

Bug 19865: Add back horizontal scroll bar

To test:
1. Do a Z39.50/SRU search
2. In the search results click on MARC to get the MARC preview. Choose
   something with lots of MARC data so it is both wide and long.
3. See the Y axis scrollbar
4. You must scroll bottom of the modal to see the X axis scrollbar,
   annoying.
5. Apply patch
6. Try steps 1-4 again. This time you should see the X axis scrollbar
   without having to scroll to the bottom.
7. It's not a bad idea to test in multiple browsers.

Note: I also put the CSS onto multiple lines to increase readability

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>