There is also another Object Style "Minimal Slide Control".
Does anyone have clue what this one does?
As far as I understand, it does nothing special. It's just a different style, meaning different colors for font or background. I think the minimal style has by default a transparent background, and transparent lines.
Take a look at buttons. You will see a wider selection. It seems they wanted to have some variety within each theme. Think of them as child records for each them and each layout object.