startup optimizations

Author: willmcgugan

src/textual/app.py

@@ -791,8 +791,8 @@ def __init__(
         perform work after the app has resumed.
         """
 
-        self.set_class(self.current_theme.dark, "-dark-mode")
-        self.set_class(not self.current_theme.dark, "-light-mode")
+        self.set_class(self.current_theme.dark, "-dark-mode", update=False)
+        self.set_class(not self.current_theme.dark, "-light-mode", update=False)
 
         self.animation_level: AnimationLevel = constants.TEXTUAL_ANIMATIONS
         """Determines what type of animations the app will display.

src/textual/dom.py

@@ -1684,9 +1684,9 @@ def set_class(self, add: bool, *class_names: str, update: bool = True) -> Self:
             Self.
         """
         if add:
-            self.add_class(*class_names, update=update and self.is_attached)
+            self.add_class(*class_names, update=update)
         else:
-            self.remove_class(*class_names, update=update and self.is_attached)
+            self.remove_class(*class_names, update=update)
         return self
 
     def set_classes(self, classes: str | Iterable[str]) -> Self:

src/textual/screen.py

@@ -1325,6 +1325,7 @@ def _on_screen_resume(self) -> None:
         """Screen has resumed."""
         if self.app.SUSPENDED_SCREEN_CLASS:
             self.remove_class(self.app.SUSPENDED_SCREEN_CLASS)
+
         self.stack_updates += 1
         self.app._refresh_notifications()
         size = self.app.size
@@ -1340,10 +1341,11 @@ def _on_screen_resume(self) -> None:
                         self.set_focus(widget)
                         break
 
-        self._compositor_refresh()
-        self.app.stylesheet.update(self)
-        self._refresh_layout(size)
-        self.refresh()
+        if self.is_attached:
+            self._compositor_refresh()
+            self.app.stylesheet.update(self)
+            self._refresh_layout(size)
+            self.refresh()
 
     def _on_screen_suspend(self) -> None:
         """Screen has suspended."""