Saying I have an `input type="file"` field. One can drop a file on this `input`(like in Firefox) instead of clicking "browse" and selecting the file.

Now, I want to customize it a bit, by changing the field's background color when one is about to drop a file in the `input`. I cannot really use `:hover` since it matches even when you're not drag&dropping. Is there a CSS (pseudo-class) to do that? 

And is there a CSS way to style different if the file being dropped is not accepted and if it is? Say, if the field accepts only PNG files using `accept` attributes, I would make the field green if you're about to drop a PNG file on it, and red if that's another type of file. 

Is there a *CSS* way to do these today? Is there a planned way to do so in *CSS* (like in upcoming specs/in current specs but not implements anywhere)?