There's a problem with embedding in the latest release when using #theme=night.
The black background only extends the length of the iframe. Scrolling beyond that has a white background.
For test, I created two simple shared dashboards and embedded them in an iframe. In each picture, I've scrolled down to show the bit just beyond the initial iframe view.
In 0.46:
Black to the bottom.
In 0.47:
Background behind the questions is white after the first view.