Non-transparent plot background

[aazuspan]

The switch from go.Figure to go.FigureWidget to include interactive buttons caused an unintended side effect of changing plot background color from transparent to white. This is caused by an inconsistency between the two classes (see plotly/plotly.py#3811).

If there's not a workaround or fix, we may just have to live with an opaque background. I guess there are worse things.

[aazuspan]

If I can inject some CSS, this is fixable with:

.cell-output-ipywidget-background {
   background-color: transparent !important;
}

See microsoft/vscode-jupyter#9403