How to keep FancyBox away from top-left corner of window?

My FancyBox is large, but I'd like it to keep a minimum distance from the top-left corner of the window. So that even when the browser window is small, you can still tell there is a pop-up FancyBox by seeing the dimmed background page and FancyBox borders.

(0,0) top-left of page
.------------------------
|    dy
| dx ***************(X)
开发者_Python百科|    *
|    * (FancyBox)
|    *

I'd like to give dx and dy minimum values, e.g. dx>50, dy>50 even when the browser is re-sized. At the moment it doesn't do that, where should I set dx & dy?

use the margin option.