There are no official and specific Church norms or requirement for lay persons who attend Mass mentioned in Canon Law or the Sacramentary. Surely for priests and other clergy there are many rules and norms but I am unaware of any currently binding norms for the laity. Although the veils were once required for women, the 1917 Code of Canon Law was abrogated and the current code is silent on any requirement. However, decency and propriety must be observed.
Note: The above photo is from a circular of the Archdiocese of Manila.
Addendum: During summer in Rome, there are tourists who visit the churches with improper attire. A church personnel is always ready to get their attention; and for ladies they usually give them an improvised alampay and/or skirt.
Circular 2007 – 23
Ministry for Liturgical Affairs
Roman Catholic Archdiocese of Manila