The `offline=True` kwarg in `ipyvolume.embed.embed_html()` is failing to save the file at https://unpkg.com/jupyter-threejs@2.0.1/dist/index.js locally as `js/jupyter-threejs.js` Copying that file manually into `js/jupyter-threejs.js` fixes the issue and allows offline viewing. I'm using ipyvolume installed from master branch: 0.5.2-dev.1