unified events and messages

docs/examples/light_dark.py

@@ -5,17 +5,15 @@ from textual.widgets import Button
 class ButtonApp(App):
 
     CSS = """
-
     Button {
         width: 100%;
     }
-
     """
 
     def compose(self):
         yield Button("Lights off")
 
-    def handle_pressed(self, event):
+    def on_button_pressed(self, event):
         self.dark = not self.dark
         self.bell()
         event.button.label = "Lights ON" if self.dark else "Lights OFF"