Default style params

[banesullivan]

It'd be nice to have a way to set the default styling of the widget. I'm thinking this might be best done through an rcParams dict. This would help avoid passing **kwargs around between libs that use this (e.g. PyVista).

An example:

...
VBox([w], layout=Layout(width='50%', border='solid'))

[banesullivan]

Actually this may be something that should just be done downstream (in PyVista) or by the user of this lib as the widget here is going to be often used as a part of an "app" embedded in a layout with other widgets and that will need to be customized.