Clean up styles

I've begun the work of making the implementation of style methods more uniform and correct, but this got to be so big that I decided to stop half-way.

This PR will represent "cleaning up" `arc` - `list_box` (using the list in #711).

I'll make lots of inline comments on what I considered "cleaning" and I'm eager to hear feedback.
There are quite a few places where I was setting the style hash directly. But really, we want those changes to be run through the style method so that `update_style` can trigger a redraw.