Not to stop anyone from adding more information, but this topic has been discussed a number of times in the past, usually in the context of certain pieces of clothing. Here are some highlights:
/u/mimicofmodes has written a couple of answers mentioning the casualization of clothes, for example suits and how our idea of "formal wear" has changed over time as well as the rise of jeans
/u/chocolatepot explains how hats fell out of style
/u/rocketsocks writes about the history of t-shirts and shirts with logos
/u/colevintage describes the history of suits