"Modern" is a somewhat fraught word. In this case, I'm using it to describe the period of time in which automotive travel and electronic communication (starting with radio, because telegrams are electric but not electronic) are ascendant. Within that term, I generally group things by decade, though there's also usually a bit over overlap at the edges of the periods.
Honestly, it's taken me a long time to get into working in modern dress, mostly because I found them to be a bit boring. It wasn't until much later in my career as a seamstress that I began to appreciate the simplicity of an outfit that you can make in a weekend, and furnish with underthings from thrift stores or your own closet. But I'm picking up speed now!