Women must always cover their knees and shoulders (but you'll be allowed inside most temples if you use a scarf to cover your shoulders). Men can wear shorts to most temples. There are no specific rules for footwear, but bear in mind that you'll be asked to walk barefoot in many temples.
Can you wear shorts to Basilica?
The Dress Code in the Vatican CityPeter's Basilica. Its basic code is for both men and women both need to cover their knees and upper arms. They prohibit wearing shorts or skirts above the knee, sleeveless tops, and low-cut shirts. Men must take their hats off before entering whereas women may continue wearing theirs.