I still don't like how they made the macOS sidebar feel like it floats over content. I don't want it to be translucent. It should feel like it "cuts" the main content and is a sibling of it, not an overlay.
For me, the mental model is so much simpler if they're sibling views. Making a change in selection in the sidebar completely changes what you see in the other view, so having them separate things makes more sense. It's more than an aesthetic thing; it's the user's conceptual model. #wwdc



