Can somebody find what a Pope said about the necklines of women's dress in France during the 18th century? Look at portraits of Queen Marie Antoinette.
Women, especially, have a hard time going against the trends of the age. Maybe it takes a special grace these days to dress with the standards mentioned above.
The Pope is not required to make a declaration on every moral question, much less on what we all know from the law of God written on our hearts, and from the Catechism. Modesty is one of those laws written upon the hearts of all.
It is grace that enables us to do any good at all, whether male or female. If a woman finds it difficult to dress modestly, she must pray for the strength to obey God in His command through the Pope. St. Alphonsus (relying on Scripture, Church Fathers, etc.) teaches that all graces we receive from God are only obtained through prayer, with the exception of certain special graces such as the grace of the Faith and conversion. Hence, there is no excuse.
“In all thy works remember thy last end, and thou shalt never sin.”— Ecclesiasticus 7:40