Add drop zone while dragging file over

[auto200]

Clear indication of drag and drop functionality

[Ciremun]

Hello!~ I've tested this on my machine Issues: Flickers or doesn't appear when dropping to center of the page Sometimes doesn't appear, but scrolls the page up or down, depending on mouse position

The attached video shows the flicker issue Please take a look at this example, it fixes the issues

https://user-images.githubusercontent.com/38132413/117087879-79144c00-ad59-11eb-9b9e-73fe63acb136.mp4

[auto200]

Hey @Ciremun Thank you for testing it out, i fixed all the issues that you mentioned, although it still scrolls a bit on firefox