Dresses are, like other outer clothing, sometimes worn with underwear. A wearer of a dress is likely to wear a design of panties as innerwear, though depending on the occasion, type of material, and type of skirt for modesty separate may wear a howler over the panties.
One may usually wear a Flower Girl Dresses bra, but for modesty wearing a camisole / vest or full misdeed is also an option for the top. Dresses are sometimes worn with tights.