Styling optional nodes

[andrico1234]

I'd like to open the discussion about how optional nodes should appear when they are:

• locked
• unlocked
• selected

The appearance of the locked state may not need to change, but 'unlocked' should have a smaller degree of affordance to a required Node, to signify that it's not necessary to progress.

The appearance of the selected state should be so that in terms of the information hierarchy, it's less important than a required Node.