fix(macOS): set titlebar background color to support transparent windows with titlebar tabs

macos/Sources/Features/Terminal/TerminalController.swift

@@ -238,6 +238,14 @@ class TerminalController: NSWindowController, NSWindowDelegate,
             delegate: self
         ))
 		
+		// Give the titlebar a custom background color to account for transparent windows.
+		window.setTitlebarBackground(
+			window
+				.backgroundColor
+				.withAlphaComponent(self.ghostty.config.backgroundOpacity)
+				.cgColor
+		)
+        
         // In various situations, macOS automatically tabs new windows. Ghostty handles
         // its own tabbing so we DONT want this behavior. This detects this scenario and undoes
         // it.

macos/Sources/Features/Terminal/TerminalWindow.swift

@@ -78,6 +78,16 @@ class TerminalWindow: NSWindow {
 		}
 	}
 	
+	// Assign a background color to the titlebar area.
+	public func setTitlebarBackground(_ color: CGColor) {
+		guard let titlebarContainer = contentView?.superview?.subviews.first(where: {
+			$0.className == "NSTitlebarContainerView"
+		}) else { return }
+		
+		titlebarContainer.wantsLayer = true
+		titlebarContainer.layer?.backgroundColor = color
+	}
+	
 	private var windowButtonsBackdrop: NSView? = nil
 	
 	private func addWindowButtonsBackdrop(titlebarView: NSView, toolbarView: NSView) {