Add custom layout creation.

src/main.zig

@@ -39,6 +39,7 @@ pub fn main() u8 {
 }
 
 fn onActivate(app: *adw.Application, _: ?*anyopaque) callconv(.c) void {
+    forceDark();
     loadCss();
 
     const window = Window.create(gpa.allocator(), app) catch |err| {
@@ -48,6 +49,15 @@ fn onActivate(app: *adw.Application, _: ?*anyopaque) callconv(.c) void {
     window.present();
 }
 
+/// The window's own chrome is dark by hand in `style.css`, but stock widgets —
+/// popovers, dialogs, text entries — follow the desktop's colour scheme and
+/// would come up light against it. Layouts brought the first real dialogs into
+/// the app, which is where that mismatch became visible.
+fn forceDark() void {
+    const manager = adw.StyleManager.getDefault();
+    manager.setColorScheme(.force_dark);
+}
+
 fn loadCss() void {
     const display = gdk.Display.getDefault() orelse return;
     const provider = gtk.CssProvider.new();