macos: only color the titlebar of surfaces that border the top

macos/Sources/Features/Terminal/TerminalController.swift

@@ -227,9 +227,21 @@ class TerminalController: BaseTerminalController {
 
         guard window.hasStyledTabs else { return }
 
-        // The titlebar is always updated. We don't need to worry about opacity
-        // because we handle it here.
-        let backgroundColor = OSColor(focusedSurface?.backgroundColor ?? surfaceConfig.backgroundColor)
+        // Our background color depends on if our focused surface borders the top or not.
+        // If it does, we match the focused surface. If it doesn't, we use the app
+        // configuration.
+        let backgroundColor: OSColor
+        if let surfaceTree {
+            if let focusedSurface, surfaceTree.doesBorderTop(view: focusedSurface) {
+                backgroundColor = OSColor(focusedSurface.backgroundColor ?? derivedConfig.backgroundColor)
+            } else {
+                // We don't have a focused surface or our surface doesn't border the
+                // top. We choose to match the color of the top-left most surface.
+                backgroundColor = OSColor(surfaceTree.topLeft().backgroundColor ?? derivedConfig.backgroundColor)
+            }
+        } else {
+            backgroundColor = OSColor(self.derivedConfig.backgroundColor)
+        }
         window.titlebarColor = backgroundColor.withAlphaComponent(surfaceConfig.backgroundOpacity)
 
         if (window.isOpaque) {
@@ -677,13 +689,16 @@ class TerminalController: BaseTerminalController {
     }
 
     private struct DerivedConfig {
+        let backgroundColor: Color
         let macosTitlebarStyle: String
 
         init() {
+            self.backgroundColor = Color(NSColor.windowBackgroundColor)
             self.macosTitlebarStyle = "system"
         }
 
         init(_ config: Ghostty.Config) {
+            self.backgroundColor = config.backgroundColor
             self.macosTitlebarStyle = config.macosTitlebarStyle
         }
     }

macos/Sources/Ghostty/Ghostty.SplitNode.swift

@@ -38,6 +38,16 @@ extension Ghostty {
             }
         }
 
+        func topLeft() -> SurfaceView {
+            switch (self) {
+            case .leaf(let leaf):
+                return leaf.surface
+
+            case .split(let container):
+                return container.topLeft.topLeft()
+            }
+        }
+
         /// Returns the view that would prefer receiving focus in this tree. This is always the
         /// top-left-most view. This is used when creating a split or closing a split to find the
         /// next view to send focus to.
@@ -136,6 +146,24 @@ extension Ghostty {
             }
         }
 
+        /// Returns true if the surface borders the top. Assumes the view is in the tree.
+        func doesBorderTop(view: SurfaceView) -> Bool {
+            switch (self) {
+            case .leaf(let leaf):
+                return leaf.surface == view
+
+            case .split(let container):
+                switch (container.direction) {
+                case .vertical:
+                    return container.topLeft.doesBorderTop(view: view)
+
+                case .horizontal:
+                    return container.topLeft.doesBorderTop(view: view) ||
+                        container.bottomRight.doesBorderTop(view: view)
+                }
+            }
+        }
+
         // MARK: - Sequence
 
         func makeIterator() -> IndexingIterator<[Leaf]> {

src/config/Config.zig

@@ -1518,6 +1518,13 @@ keybind: Keybinds = .{},
 /// This makes a more seamless window appearance but looks a little less
 /// typical for a macOS application and may not work well with all themes.
 ///
+/// The "transparent" style will also update in real-time to dynamic
+/// changes to the window background color, i.e. via OSC 11. To make this
+/// more aesthetically pleasing, this only happens if the terminal is
+/// a window, tab, or split that borders the top of the window. This
+/// avoids a disjointed appearance where the titlebar color changes
+/// but all the topmost terminals don't match.
+///
 /// The "tabs" style is a completely custom titlebar that integrates the
 /// tab bar into the titlebar. This titlebar always matches the background
 /// color of the terminal. There are some limitations to this style:
@@ -1536,11 +1543,6 @@ keybind: Keybinds = .{},
 /// but its one I think is the most aesthetically pleasing and works in
 /// most cases.
 ///
-/// BUG: If a separate light/dark mode theme is configured with "theme",
-/// then `macos-titlebar-style = transparent` will not work correctly. To
-/// avoid ugly titlebars, `macos-titlebar-style` will become `native` if
-/// a separate light/dark theme is configured.
-///
 /// Changing this option at runtime only applies to new windows.
 @"macos-titlebar-style": MacTitlebarStyle = .transparent,