No background transparency with go.FigureWidget

[aazuspan]

Hi Plotly devs, thanks for maintaining this awesome package. I'm running 5.9.0 and hit an inconsistency between how go.Figure and go.FigureWidget handle background colors.

With a go.Figure, you can set paper_bgcolor to get a transparent background (note that in the screenshot my IDE has a dark background).

go.Figure(layout=dict(paper_bgcolor="rgba(0, 0, 0, 0)"))

With a go.FigureWidget, there seems to be a white background that isn't controlled by paper_bgcolor.

go.FigureWidget(layout=dict(paper_bgcolor="rgba(0, 0, 0, 0)"))

Any ideas to achieve a transparent background with a FigureWidget would be appreciated!