Allow selecting theme in url param

[dhirschfeld]

I'd like to use the dark theme when previewing my voila dashboard in JupyterLab. It doesn't appear this is possible?

I tried passing it as an argument to the url ?voila-template=gridstack&theme=dark but that didn't work :/

[dhirschfeld]

Related to voila-dashboards/voila#606 (comment)

Ideally voila gridstack would pick up the theme used by JupyterLab but allow it to be overridden by specifying the theme to use in a url param or the notebook metadata