SinglePaneLayout wrapped the main content area in `.padding(12.dp)`,
leaving a visible strip of the window background around every screen.
On macOS with the theming updates this strip became very noticeable:
conversation list, chat content, and the NavigationRail no longer
shared a single edge, and you could see `#F5F5F7` framing the whole
content block.
Native desktop apps don't frame content like that — padding is added
inside cards / lists / dialogs, not around the window content area.
Removing the wrapper padding lets the Messages two-column layout
(surfaceContainer sidebar + surface chat) run edge-to-edge.
https://claude.ai/code/session_01NufduPfZvYQVYwLkbCjCUo
Claude
979c262d87