QFQ

"Drag & Drop or" should not be hardcoded, but instead set with a parameter. It should be possible to leave the text empty ("Drag & Drop" is arguably unnecessary information for the user) or set a custom text.
Increase height of FE and gaps between button and border.

You can click anywhere inside the upload FE to trigger the upload dialog. This means that the button does not have any special purpose regarding functionality. With customizable text (see above) the button could theoretically be left out.