firewall: Fix missing CSS for add services
firewall: Fix missing CSS for add services

Fixes #17615

martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit