by gtk_css_provider_new

Don't hesitate to revert this one but only if there's a patch
to fix it.
Change-Id: Id91fefb689326a31e029a788bd3729e670fe3100
Reviewed-on: https://gerrit.libreoffice.org/60915Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Julien Nabet <serval2412@yahoo.fr>