new layout geometry

examples/new.py

@@ -0,0 +1,24 @@
+from textual import events
+from textual.app import App, Bind
+from textual.widgets import Header, Placeholder, MarkdownViewer
+
+
+class MyApp(App):
+    KEYS = {
+        "q, ctrl+c": Bind("quit"),
+        "b": Bind("view.toggle('left')", "Toggle Sidebar"),
+    }
+
+    async def on_load(self, event: events.Load) -> None:
+        self.bind(self.KEYS)
+
+    async def on_startup(self, event: events.Startup) -> None:
+        await self.view.mount(
+            header=Header(),
+            left=Placeholder(),
+            body=MarkdownViewer("readme.md"),
+        )
+
+
+app = MyApp(title="Simple Textual App")
+app.run()