Styling (far, fas) for fontawesome icons

[swelborn]

trafficstars

Using ipywidgets 8.

There are multiple versions of the same icon on fontawesome. For ex. "square" can be specified by far or fas to change whether it is filled or not.

However, this:

from ipywidgets import *
a = Button(icon="fas square")
b = Button(icon="far square")
HBox([a, b])

produces this:

Is this already possible and I just don't know how to do it?