dressed to the nines

(idiomatic) Very fancily or formally dressed; wearing very showy or splendid clothing.

Example: He arrived at the gala, dressed to the nines in his top hat and tails.
1976, Tim Rice, "Don't Cry For Me Argentina"
  All you will see is a girl you once knew, although she's dressed up to the nines, at sixes and sevens with you.