Set loading image on replaced elements instead of on their descendants

Replaced elements do not have "::after" nor "::before" pseudo-elements,
so the regular loading icon needs to be shown using a background image
instead of the default "::after" pseudo-element approach. However, the
CSS rules were not applied on the replaced elements themselves, but on
their descendants. As the descendants might have support for
pseudo-elements the rules were fixed to be applied on the replaced
elements, and only on the replaced elements.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>