Riccardo Mori goes deep into Liquid Glass:
In Leopard — but also in other versions of Mac OS that came before and after, at least until the Big Sur redesign — the Finder window structure and hierarchy is well defined and self-evident: the main chrome is the area above and below the window’s contents, represented by the title bar, the toolbar below it, and then the status bar at the bottom of the window. The chrome clearly frames the Finder window. Then, inside, we have the sidebar on the left, and the folder contents on the right; it’s more or less the same structure as a Web browser. The folder contents are the Web page, the sidebar shows a lists of places (or bookmarks if you like), the status bar on the bottom works in a similar fashion as a browser’s status bar. It’s a clear representation of what is content versus what are controls. Content and controls don’t bleed into each other’s territory.
But in the world of Alan Dye, it’s all content inside roundrects with thin bezels, and controls hover above it in quasi-borderless states, options become little treasures hidden behind ‘More…’ icons (the circle with three dots in it), panels and windows get deconstructed like those ‘designer dishes’ you see in fancy restaurants.