"Perfectly" means "completely" or "totally". It's used with these phrases:

• perfectly normal
• perfectly good
• to be perfectly honest,
• perfectly white
• sit perfectly still

You use the phrase "perfectly safe" when you're talking about something that people think isn't safe. You say that it is "perfectly safe", meaning that you don't think there are any problems with it:

It's perfectly safe to take a healthy newborn out of the house as soon as you're ready.

"Perfectly good" is used in the same way.