login: require CSS flex & grid support
login: require CSS flex & grid support

Closes #10569

andreasn/cockpit,moraleslazaro/cockpit,garrett/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,garrett/cockpit,martinpitt/cockpit,deryni/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,garrett/cockpit,mvollmer/cockpit,deryni/cockpit,cockpituous/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpituous/cockpit,mvollmer/cockpit,andreasn/cockpit,martinpitt/cockpit,deryni/cockpit,mvollmer/cockpit,deryni/cockpit,garrett/cockpit,andreasn/cockpit,andreasn/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpituous/cockpit,andreasn/cockpit,andreasn/cockpit,cockpituous/cockpit,deryni/cockpit,andreasn/cockpit