Everyone at the party was dressed to the nines.
dressed to the nines
idiomVery fancily or formally dressed; wearing very showy or splendid clothing.
Origin
From dressed + to the nines; first recorded in the 1800s.
Since it was a formal wedding, she made sure to be dressed to the nines in her best silk gown.
The guests arrived at the gala dressed to the nines, their expensive jewelry sparkling under the bright lights of the grand ballroom.