Qur’ān Surah 24:31:
"And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their beauty and ornaments except what (must ordinarily) appear thereof; that they should draw their veils over their bosoms and not display their beauty except to their husbands, their fathers, their husband's fathers, their sons, their husbands' sons, their brothers or their brothers' sons, or their sisters' sons, or their women, or the slaves whom their right hands possess, or male servants free of physical needs, or small children who have no sense of the shame of sex; and that they should not strike their feet in order to draw attention to their hidden ornaments. And O ye Believers! turn ye all together towards Allah, that ye may attain Bliss."
Keep in mind, that you do not just have to DRESS modestly, rather have to BEHAVE modestly as well. Lower your gaze and remember Allah Subhanahu wa Ta'Alaa in every single moment.
As-Salamu Alaikum wa Rahmatullahi wa Barakatahu.