What modesty actually means, and what it does not.
Dress as you would to meet someone you owe your life to, allowing for what you honestly own.
Modesty is a virtue about honesty and charity in how you present yourself, not a dress code with hemlines.
Never let clothing keep you from Mass. Coming as you are beats staying home well dressed.
The Catechism calls modesty a part of temperance and says it protects the mystery of the person. That is not shame about the body. It is a refusal to reduce a person, yourself included, to a surface.
Christian writers from the second century on urged restraint in dress against the display culture of the Roman city, usually alongside warnings about wealth rather than about the body.
Specific rules have come and gone by century and culture. The virtue underneath them has not.
Modesty is a virtue and so is binding on everyone. Any particular custom about clothing is not, and using it to police strangers in a parish is a failure of charity that does more harm than a short sleeve ever did.