u/Ashamed_Floor_2283

I'm building a SwiftUI app on macOS 26 with NavigationSplitView (sidebar + detail). In non-fullscreen mode, the titlebar looks clean. But in fullscreen, AppKit's NSToolbarFullScreenWindow paints the default chrome color (white in light mode, dark-gray in dark) across only the detail column portion of the titlebar — the sidebar column still shows its glass material above. This creates an obvious visual cutoff at the sidebar/detail boundary that screams broken.

Non-fullscreen: Looks normal. The titlebar background is consistent with the rest of the window.

Fullscreen: The titlebar detail column turns dark-gray (in dark mode).

I'm building a SwiftUI app on macOS 26 with NavigationSplitView (sidebar + detail). In non-fullscreen mode, the titlebar looks clean. But in fullscreen, AppKit's NSToolbarFullScreenWindow paints the default chrome color (white in light mode, dark-gray in dark) across only the detail column portion of the titlebar — the sidebar column still shows its glass material above. This creates an obvious visual cutoff at the sidebar/detail boundary that screams broken.

Non-fullscreen: Looks normal. The titlebar background is consistent with the rest of the window.

Fullscreen: The titlebar detail column turns dark-gray (in dark mode).

I'm building a SwiftUI app on macOS 26 with NavigationSplitView (sidebar + detail). In non-fullscreen mode, the titlebar looks clean. But in fullscreen, AppKit's NSToolbarFullScreenWindow paints the default chrome color (white in light mode, dark-gray in dark) across only the detail column portion of the titlebar — the sidebar column still shows its glass material above. This creates an obvious visual cutoff at the sidebar/detail boundary that screams broken.

Fullscreen: The titlebar detail column turns dark-gray (in dark mode).

Non-fullscreen: Looks normal. The titlebar color is consistent with the rest of the window.