This is great work, the interactive demo is a good way to show it off too. It’s fun to drag the window over the moon.

That said I dislike the use of frosted glass in user interface design, and feel it was a step backwards for Mac OS when it was added. Designers (hypocritically including myself - I use it too sometimes) are so seduced by it. But in practice it’s never ideal. Especially if the content behind the panel is dynamic or user generated.

It’s the brushed metal of the 2010s, I’m surprised that it leaked out of Windows Vista into everything else!

Why isn't it "ideal"? Visual design is mostly about personal preferences about what looks good, rather than serving any practical purpose. Yes, design also impacts functionality, but it mostly exists to make the user experience more pleasant.

If you ask me, skeuomorphism makes interfaces more pleasing to use than the minimalistic trend of the past decade+, where everything must be flat. It adds a visual flourish that replicates surfaces and materials we're used to from the real world, making interfaces more familiar and approachable. From a practical standpoint, flat design makes it hard to distinguish elements and their state, whereas when we had 3D buttons, brushed metal and frosted glass, this was very clear.

I think the pendulum is swinging back now, as more designers are shunning the flat look, so hopefully we'll see a resurgence of more human-friendly UIs.

I'm not a UI designer so honest question: is the problem the use of aesthetics, like frosted glass or brushed metal, in UI design or is it that in pursuit of presenting such interfaces some designers lost the visual queues needed to indicate where controls are and what they do?

My terminal windows have had a slight transparency for years, but now I've been rethinking it

Ironically previous versions of macOS also used brushed metal heavily