gtk: enable window-title-font-family (#4560)

src/apprt/gtk/App.zig

@@ -1002,13 +1002,19 @@ fn loadRuntimeCss(
             \\  color: rgb({[r]d},{[g]d},{[b]d});
             \\  background: rgb({[r]d},{[g]d},{[b]d});
             \\}}
-        ,
+        , .{
-            .{
             .r = color.r,
             .g = color.g,
             .b = color.b,
-            },
+        });
-        );
+    }
+
+    if (config.@"window-title-font-family") |font_family| {
+        try writer.print(
+            \\.window headerbar {{
+            \\  font-family: "{[font_family]s}";
+            \\}}
+        , .{ .font_family = font_family });
     }
 
     if (version.atLeast(4, 16, 0)) {

src/apprt/gtk/ClipboardConfirmationWindow.zig

@@ -64,6 +64,7 @@ fn init(
     c.gtk_window_set_title(gtk_window, titleText(request));
     c.gtk_window_set_default_size(gtk_window, 550, 275);
     c.gtk_window_set_resizable(gtk_window, 0);
+    c.gtk_widget_add_css_class(@ptrCast(@alignCast(gtk_window)), "window");
     c.gtk_widget_add_css_class(@ptrCast(@alignCast(gtk_window)), "clipboard-confirmation-window");
     _ = c.g_signal_connect_data(
         window,

src/apprt/gtk/ConfigErrorsWindow.zig

@@ -55,6 +55,7 @@ fn init(self: *ConfigErrors, app: *App) !void {
     c.gtk_window_set_default_size(gtk_window, 600, 275);
     c.gtk_window_set_resizable(gtk_window, 0);
     c.gtk_window_set_icon_name(gtk_window, build_config.bundle_id);
+    c.gtk_widget_add_css_class(@ptrCast(@alignCast(gtk_window)), "window");
     c.gtk_widget_add_css_class(@ptrCast(@alignCast(gtk_window)), "config-errors-window");
     _ = c.g_signal_connect_data(window, "destroy", c.G_CALLBACK(&gtkDestroy), self, null, c.G_CONNECT_DEFAULT);
 

src/apprt/gtk/Window.zig

@@ -99,6 +99,7 @@ pub fn init(self: *Window, app: *App) !void {
     self.window = gtk_window;
     c.gtk_window_set_title(gtk_window, "Ghostty");
     c.gtk_window_set_default_size(gtk_window, 1000, 600);
+    c.gtk_widget_add_css_class(@ptrCast(gtk_window), "window");
     c.gtk_widget_add_css_class(@ptrCast(gtk_window), "terminal-window");
 
     // GTK4 grabs F10 input by default to focus the menubar icon. We want

src/apprt/gtk/inspector.zig

@@ -143,6 +143,7 @@ const Window = struct {
         c.gtk_window_set_title(gtk_window, "Ghostty: Terminal Inspector");
         c.gtk_window_set_default_size(gtk_window, 1000, 600);
         c.gtk_window_set_icon_name(gtk_window, build_config.bundle_id);
+        c.gtk_widget_add_css_class(@ptrCast(@alignCast(gtk_window)), "window");
         c.gtk_widget_add_css_class(@ptrCast(@alignCast(gtk_window)), "inspector-window");
 
         // Initialize our imgui widget

src/config/Config.zig

@@ -1077,7 +1077,10 @@ keybind: Keybinds = .{},
 
 /// The font that will be used for the application's window and tab titles.
 ///
-/// This is currently only supported on macOS.
+/// If this setting is left unset, the system default font will be used.
+///
+/// Note: any font available on the system may be used, this font is not
+/// required to be a fixed-width font.
 @"window-title-font-family": ?[:0]const u8 = null,
 
 /// The theme to use for the windows. Valid values: