Fix Extended Maintenance badge background
Fix Extended Maintenance badge background

In patch I2aea17466ff3da652ba01d98def635d744e67fbb the corresponding
css background was not created. This patch sets the same background as
the badge of 'maintained' releases has.

Change-Id: Ia6c18857e89b384a334eb84c629e6e5d7249fa9e

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals