Issue with example notebook shown in binder

[CasperWA]

When pressing the button to choose Li and H, the elements turn blue in the periodic table. A color which is otherwise not reachable through normal toggling. Maybe you are missing to update some traitlets or other? I am not completely sure. The issue only occurs for the binder in this repository, for the similar binder in the aiidalab-voila template, this didn't seem to be an issue. However, the state was random (or at least different) in that one (maybe also here).

[giovannipizzi]

I mentioned this issue in osscar-org/widget-periodictable#4 - let's continue the discussion there as it's a problem of the widget and not of the template of voila