macos: sync NSAppearance for app based on window-theme setting

macos/Sources/AppDelegate.swift

@@ -187,6 +187,9 @@ class AppDelegate: NSObject, ObservableObject, NSApplicationDelegate, GhosttyApp
         // Config could change keybindings, so update our menu
         syncMenuShortcuts()
         
+        // Config could change window appearance
+        syncAppearance()
+        
         // If we have configuration errors, we need to show them.
         let c = ConfigurationErrorsController.sharedInstance
         c.model.errors = state.configErrors()
@@ -197,6 +200,23 @@ class AppDelegate: NSObject, ObservableObject, NSApplicationDelegate, GhosttyApp
         }
     }
     
+    /// Sync the appearance of our app with the theme specified in the config.
+    private func syncAppearance() {
+        guard let theme = ghostty.windowTheme else { return }
+        switch (theme) {
+        case "dark":
+            let appearance = NSAppearance(named: .darkAqua)
+            NSApplication.shared.appearance = appearance
+            
+        case "light":
+            let appearance = NSAppearance(named: .aqua)
+            NSApplication.shared.appearance = appearance
+            
+        default:
+            NSApplication.shared.appearance = nil
+        }
+    }
+    
     //MARK: - Dock Menu
     
     private func reloadDockMenu() {

macos/Sources/Ghostty/AppState.swift

@@ -71,6 +71,16 @@ extension Ghostty {
             _ = ghostty_config_get(config, &v, key, UInt(key.count))
             return v;
         }
+        
+        /// The window theme as a string.
+        var windowTheme: String? {
+            guard let config = self.config else { return nil }
+            var v: UnsafePointer<Int8>? = nil
+            let key = "window-theme"
+            guard ghostty_config_get(config, &v, key, UInt(key.count)) else { return nil }
+            guard let ptr = v else { return nil }
+            return String(cString: ptr)
+        }
 
         init() {
             // Initialize ghostty global state. This happens once per process.