Bug 23791: (follow-up) Add missing CSS changes

Bug 23791: (follow-up) Add missing CSS changes

This patch adds OPAC CSS changes which were missing from the original
patch. It also adds a missing title attribute to the Twitter link.

To test, apply the patch and regenerate the OPAC SCSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

Follow the previous test plan.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>