[quote=@NekoMizu]
I am in the understanding that steampunk is like a future/past mix, but what about modern/past mix? Heck, what about all three combined? Would those still be considered steampunk or would it have a new name entirely? Has the idea of mixing modern days with medieval ages been done. Probably. If so, then can you tell what has done this?
[/quote]

If we're going to be super duper technical... 

While Steampunk is considered a sub-genre of science fiction, it often takes place in an alternate past where industrial steam powered machinery progressed a lot further and became mainstream. So it's not science fiction because it takes place in the future, but because these worlds rely on steam powered machinery that never existed. Science fiction is actually defined by the scientific advancements of it's world, which are [i]usually[/i] in the distant future.

As for a modern/Sci-fi/Fantasy mix, the closest things I can think of is [url=https://en.wikipedia.org/wiki/Magic_realism]Magic Realism[/url]. 

As Aix said, the Japanese love to do modern fantasy. It's hard to look at an anime list and not see at least one like that.