diff --git a/src/apprt/gtk/App.zig b/src/apprt/gtk/App.zig
index 6d8bdce27..80749437f 100644
--- a/src/apprt/gtk/App.zig
+++ b/src/apprt/gtk/App.zig
@@ -70,6 +70,9 @@ x11_xkb: ?x11.Xkb = null,
 /// and initialization was successful.
 transient_cgroup_base: ?[]const u8 = null,
 
+/// CSS Provider for any styles based on ghostty configuration values
+css_provider: *c.GtkCssProvider,
+
 pub fn init(core_app: *CoreApp, opts: Options) !App {
     _ = opts;
 
@@ -268,6 +271,9 @@ pub fn init(core_app: *CoreApp, opts: Options) !App {
         );
     }
 
+    const css_provider = c.gtk_css_provider_new();
+    try loadRuntimeCss(&config, css_provider);
+
     return .{
         .core_app = core_app,
         .app = app,
@@ -280,6 +286,7 @@ pub fn init(core_app: *CoreApp, opts: Options) !App {
         // This means that another instance of the GTK app is running and
         // our "activate" call above will open a window.
         .running = c.g_application_get_is_remote(gapp) == 0,
+        .css_provider = css_provider,
     };
 }
 
@@ -327,6 +334,7 @@ pub fn reloadConfig(self: *App) !?*const Config {
 fn syncConfigChanges(self: *App) !void {
     try self.updateConfigErrors();
     try self.syncActionAccelerators();
+    try loadRuntimeCss(&self.config, self.css_provider);
 }
 
 /// This should be called whenever the configuration changes to update
@@ -379,6 +387,33 @@ fn syncActionAccelerator(
     );
 }
 
+fn loadRuntimeCss(config: *const Config, provider: *c.GtkCssProvider) !void {
+    const fill: Config.Color = config.@"unfocused-split-fill" orelse config.background;
+    const fmt =
+        \\widget.unfocused-split {{
+        \\ opacity: {d:.2};
+        \\ background-color: rgb({d},{d},{d});
+        \\}}
+    ;
+    // The length required is always less than the length of the pre-formatted string:
+    // -> '{d:.2}' gets replaced with max 4 bytes (0.00)
+    // -> each {d} could be replaced with max 3 bytes
+    var css_buf: [fmt.len]u8 = undefined;
+
+    const css = try std.fmt.bufPrintZ(
+        &css_buf,
+        fmt,
+        .{
+            config.@"unfocused-split-opacity",
+            fill.r,
+            fill.g,
+            fill.b,
+        },
+    );
+    // Clears any previously loaded CSS from this provider
+    c.gtk_css_provider_load_from_data(provider, css, @intCast(css.len));
+}
+
 /// Called by CoreApp to wake up the event loop.
 pub fn wakeup(self: App) void {
     _ = self;
diff --git a/src/apprt/gtk/Split.zig b/src/apprt/gtk/Split.zig
index 148651d4b..622db61fe 100644
--- a/src/apprt/gtk/Split.zig
+++ b/src/apprt/gtk/Split.zig
@@ -77,6 +77,7 @@ pub fn init(
         .parent = &sibling.core_surface,
     });
     errdefer surface.destroy(alloc);
+    sibling.dimSurface();
 
     // Create the actual GTKPaned, attach the proper children.
     const orientation: c_uint = switch (direction) {
diff --git a/src/apprt/gtk/Surface.zig b/src/apprt/gtk/Surface.zig
index 62a432c9e..05fce6905 100644
--- a/src/apprt/gtk/Surface.zig
+++ b/src/apprt/gtk/Surface.zig
@@ -325,6 +325,9 @@ gl_area: *c.GtkGLArea,
 /// If non-null this is the widget on the overlay that shows the URL.
 url_widget: ?URLWidget = null,
 
+/// If non-null this is the widget on the overlay which dims the surface when it is unfocused
+unfocused_widget: ?*c.GtkWidget = null,
+
 /// Any active cursor we may have
 cursor: ?*c.GdkCursor = null,
 
@@ -590,6 +593,10 @@ pub fn deinit(self: *Surface) void {
     // Free all our GTK stuff
     c.g_object_unref(self.im_context);
     if (self.cursor) |cursor| c.g_object_unref(cursor);
+    if (self.unfocused_widget) |widget| {
+        c.gtk_overlay_remove_overlay(self.overlay, widget);
+        self.unfocused_widget = null;
+    }
 }
 
 // unref removes the long-held reference to the gl_area and kicks off the
@@ -1809,6 +1816,12 @@ fn gtkFocusEnter(_: *c.GtkEventControllerFocus, ud: ?*anyopaque) callconv(.C) vo
     // Notify our IM context
     c.gtk_im_context_focus_in(self.im_context);
 
+    // Remove the unfocused widget overlay, if we have one
+    if (self.unfocused_widget) |widget| {
+        c.gtk_overlay_remove_overlay(self.overlay, widget);
+        self.unfocused_widget = null;
+    }
+
     // Notify our surface
     self.core_surface.focusCallback(true) catch |err| {
         log.err("error in focus callback err={}", .{err});
@@ -1823,12 +1836,29 @@ fn gtkFocusLeave(_: *c.GtkEventControllerFocus, ud: ?*anyopaque) callconv(.C) vo
     // Notify our IM context
     c.gtk_im_context_focus_out(self.im_context);
 
+    // We only dim the surface if we are a split
+    switch (self.container) {
+        .split_br,
+        .split_tl,
+        => self.dimSurface(),
+        else => {},
+    }
+
     self.core_surface.focusCallback(false) catch |err| {
         log.err("error in focus callback err={}", .{err});
         return;
     };
 }
 
+/// Adds the unfocused_widget to the overlay. If the unfocused_widget has already been added, this
+/// is a no-op
+pub fn dimSurface(self: *Surface) void {
+    if (self.unfocused_widget != null) return;
+    self.unfocused_widget = c.gtk_drawing_area_new();
+    c.gtk_widget_add_css_class(self.unfocused_widget.?, "unfocused-split");
+    c.gtk_overlay_add_overlay(self.overlay, self.unfocused_widget.?);
+}
+
 fn gtkCloseConfirmation(
     alert: *c.GtkMessageDialog,
     response: c.gint,
diff --git a/src/apprt/gtk/Window.zig b/src/apprt/gtk/Window.zig
index 0cb73c407..7a3418bb4 100644
--- a/src/apprt/gtk/Window.zig
+++ b/src/apprt/gtk/Window.zig
@@ -16,6 +16,7 @@ const input = @import("../../input.zig");
 const CoreSurface = @import("../../Surface.zig");
 
 const App = @import("App.zig");
+const Color = configpkg.Config.Color;
 const Surface = @import("Surface.zig");
 const Tab = @import("Tab.zig");
 const c = @import("c.zig");
@@ -71,6 +72,11 @@ pub fn init(self: *Window, app: *App) !void {
         c.gtk_widget_set_opacity(@ptrCast(window), app.config.@"background-opacity");
     }
 
+    // Internally, GTK ensures that only one instance of this provider exists in the provider list
+    // for the display.
+    const display = c.gdk_display_get_default();
+    c.gtk_style_context_add_provider_for_display(display, @ptrCast(app.css_provider), c.GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
+
     // Use the new GTK4 header bar. We only create a header bar if we have
     // window decorations.
     if (app.config.@"window-decoration") {
diff --git a/src/config/Config.zig b/src/config/Config.zig
index e3165a988..e4de1d22e 100644
--- a/src/config/Config.zig
+++ b/src/config/Config.zig
@@ -409,8 +409,6 @@ palette: Palette = .{},
 /// is 0.15. This value still looks weird but you can at least see what's going
 /// on. A value outside of the range 0.15 to 1 will be clamped to the nearest
 /// valid value.
-///
-/// This is only supported on macOS.
 @"unfocused-split-opacity": f64 = 0.7,
 
 /// The color to dim the unfocused split. Unfocused splits are dimmed by
@@ -418,8 +416,6 @@ palette: Palette = .{},
 /// that rectangle and can be used to carefully control the dimming effect.
 ///
 /// This will default to the background color.
-///
-/// This is only supported on macOS.
 @"unfocused-split-fill": ?Color = null,
 
 /// The command to run, usually a shell. If this is not an absolute path, it'll