feat: update DemoApp to use external CSS file for demonstration

Author: CNSeniorious000

examples/textual/README.md

@@ -12,10 +12,12 @@ textual-hmr main:DemoApp
 
 ## What to Observe
 
-The app renders a short message from `message.py`.
+The app renders a short message from `message.py` and loads styles from `main.tcss`.
 
 - Change the string in `message.py` and save it.
 - The current Textual app instance will exit and restart in-process.
 - The updated message will appear immediately after restart.
+- Change `main.tcss` and save it.
+- Textual will hot-refresh the stylesheet without restarting the Python app.
 
-Because `DemoApp` is exported as an `App` subclass, `textual-hmr` also enables Textual's built-in CSS watching by default. You can tweak the inline CSS in `main.py` to compare Python-level restarts with CSS-only refreshes.
+Because `DemoApp` is exported as an `App` subclass, `textual-hmr` also enables Textual's built-in CSS watching by default. This example lets you compare Python-level restarts with TCSS-only refreshes side by side.

examples/textual/main.py

@@ -5,10 +5,7 @@
 
 
 class DemoApp(App[None]):
-    CSS = """
-    Screen { align: center middle; }
-    #panel { width: 56; padding: 1 3; border: round $accent; background: $surface; }
-    """
+    CSS_PATH = "main.tcss"
 
     def compose(self):
         yield Header()

examples/textual/main.tcss

@@ -0,0 +1,10 @@
+Screen {
+    align: center middle;
+}
+
+#panel {
+    width: 56;
+    padding: 1 3;
+    border: round $accent;
+    background: $surface;
+}