fix for dark switch (#2585)

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fixed `TreeNode.toggle` and `TreeNode.toggle_all` not posting a `Tree.NodeExpanded` or `Tree.NodeCollapsed` message https://github.com/Textualize/textual/issues/2535
 - `footer--description` component class was being ignored https://github.com/Textualize/textual/issues/2544
 - Pasting empty selection in `Input` would raise an exception https://github.com/Textualize/textual/issues/2563
+- Fix for setting dark in App `__init__` https://github.com/Textualize/textual/issues/2583
 - Fix issue with scrolling and docks https://github.com/Textualize/textual/issues/2525
 
 ### Added

src/textual/app.py

@@ -604,14 +604,7 @@ class App(Generic[ReturnType], DOMNode):
         """
         self.set_class(dark, "-dark-mode")
         self.set_class(not dark, "-light-mode")
-        try:
-            self.refresh_css()
-        except ScreenStackError:
-            # It's possible that `dark` can be set before we have a default
-            # screen, in an app's `on_load`, for example. So let's eat the
-            # ScreenStackError -- the above styles will be handled once the
-            # screen is spun up anyway.
-            pass
+        self.call_later(self.refresh_css)
 
     def get_driver_class(self) -> Type[Driver]:
         """Get a driver class for this platform.