diff --git a/sandbox/basic.py b/sandbox/basic.py
index 0778a9eed..267653581 100644
--- a/sandbox/basic.py
+++ b/sandbox/basic.py
@@ -89,7 +89,7 @@ class BasicApp(App):
 
     def on_load(self):
         """Bind keys here."""
-        self.bind("tab", "toggle_class('#sidebar', '-active')")
+        self.bind("s", "toggle_class('#sidebar', '-active')")
 
     def on_mount(self):
         """Build layout here."""
diff --git a/src/textual/app.py b/src/textual/app.py
index 0dffb9524..a2bfca31e 100644
--- a/src/textual/app.py
+++ b/src/textual/app.py
@@ -25,6 +25,7 @@ import rich.repr
 from rich.console import Console, RenderableType
 from rich.control import Control
 from rich.measure import Measurement
+from rich.protocol import is_renderable
 from rich.screen import Screen as ScreenRenderable
 from rich.segment import Segments
 from rich.traceback import Traceback
@@ -96,7 +97,9 @@ ReturnType = TypeVar("ReturnType")
 class App(Generic[ReturnType], DOMNode):
     """The base class for Textual Applications"""
 
-    css = ""
+    css = """
+
+    """
 
     def __init__(
         self,
@@ -205,7 +208,7 @@ class App(Generic[ReturnType], DOMNode):
         self.close_messages_no_wait()
 
     @property
-    def _focusable_widgets(self) -> list[Widget]:
+    def focus_chain(self) -> list[Widget]:
         """Get widgets that may receive focus"""
         widgets: list[Widget] = []
         add_widget = widgets.append
@@ -219,7 +222,7 @@ class App(Generic[ReturnType], DOMNode):
             if node is None:
                 pop()
             else:
-                if node.is_container:
+                if node.is_container and node.can_focus:
                     push(iter(node.children))
                 else:
                     if node.can_focus:
@@ -227,25 +230,25 @@ class App(Generic[ReturnType], DOMNode):
 
         return widgets
 
-    def show_focus(self) -> None:
-        """Highlight the currently focused widget."""
-        self.move_focus(0)
+    def _set_active(self) -> None:
+        active_app.set(self)
 
-    def move_focus(self, direction: int = 0) -> None:
+    def _move_focus(self, direction: int = 0) -> Widget | None:
         """Move the focus in the given direction.
 
         Args:
             direction (int, optional): 1 to move forward, -1 to move backward, or
                 0 to highlight the current focus.
         """
-
         if self._focus_timer:
+            # Cancel the timer that clears the show focus class
+            # We will be creating a new timer to extend the time until the focus is hidden
             self._focus_timer.stop_no_wait()
-        focusable_widgets = self._focusable_widgets
+        focusable_widgets = self.focus_chain
 
         if not focusable_widgets:
             # Nothing focusable, so nothing to do
-            return
+            return self.focused
         if self.focused is None:
             # Nothing currently focused, so focus the first one
             self.set_focus(focusable_widgets[0])
@@ -262,17 +265,21 @@ class App(Generic[ReturnType], DOMNode):
                     current_index = (current_index + direction) % len(focusable_widgets)
                     self.set_focus(focusable_widgets[current_index])
 
-        self._focus_timer = self.set_timer(3, self.hide_focus)
+        self._focus_timer = self.set_timer(2, self.hide_focus)
         self.add_class("-show-focus")
-        self.screen.refresh_layout()
+        return self.focused
 
-    def focus_next(self) -> None:
+    def show_focus(self) -> Widget | None:
+        """Highlight the currently focused widget."""
+        return self._move_focus(0)
+
+    def focus_next(self) -> Widget | None:
         """Focus the next widget."""
-        self.move_focus(1)
+        return self._move_focus(1)
 
-    def focus_previous(self) -> None:
+    def focus_previous(self) -> Widget | None:
         """Focus the previous widget."""
-        self.move_focus(-1)
+        return self._move_focus(-1)
 
     def hide_focus(self) -> None:
         """Hide the focus."""
@@ -483,9 +490,10 @@ class App(Generic[ReturnType], DOMNode):
         self.register(self.screen, *anon_widgets, **widgets)
         self.screen.refresh()
 
-    async def push_screen(self, screen: Screen) -> Screen:
-        self._screen_stack.append(screen)
-        return screen
+    def push_screen(self, screen: Screen | None = None) -> Screen:
+        new_screen = Screen() if screen is None else screen
+        self._screen_stack.append(new_screen)
+        return new_screen
 
     def set_focus(self, widget: Widget | None) -> None:
         """Focus (or unfocus) a widget. A focused widget will receive key events first.
@@ -493,25 +501,32 @@ class App(Generic[ReturnType], DOMNode):
         Args:
             widget (Widget): [description]
         """
-        self.log("set_focus", widget)
+        self.log("set_focus", widget=widget)
         if widget == self.focused:
-            self.log("already focused")
             # Widget is already focused
             return
 
         if widget is None:
-            if self.focused is not None:
-                focused = self.focused
-                self.focused = None
-                focused.post_message_no_wait(events.Blur(self))
-        elif widget.can_focus:
+            # No focus, so blur currently focused widget if it exists
             if self.focused is not None:
                 self.focused.post_message_no_wait(events.Blur(self))
-            if widget is not None and self.focused != widget:
+                self.focused = None
+        elif widget.can_focus:
+            if self.focused != widget:
+                if self.focused is not None:
+                    # Blur currently focused widget
+                    self.focused.post_message_no_wait(events.Blur(self))
+                # Change focus
                 self.focused = widget
+                # Send focus event
                 widget.post_message_no_wait(events.Focus(self))
 
-    async def set_mouse_over(self, widget: Widget | None) -> None:
+    async def _set_mouse_over(self, widget: Widget | None) -> None:
+        """Called when the mouse is over a nother widget.
+
+        Args:
+            widget (Widget | None): Widget under mouse, or None for no widgets.
+        """
         if widget is None:
             if self.mouse_over is not None:
                 try:
@@ -551,6 +566,10 @@ class App(Generic[ReturnType], DOMNode):
             *renderables (RenderableType, optional): Rich renderables to display on exit.
         """
 
+        assert all(
+            is_renderable(renderable) for renderable in renderables
+        ), "Can only call panic with strings or Rich renderables"
+
         prerendered = [
             Segments(self.console.render(renderable, self.console.options))
             for renderable in renderables
@@ -589,7 +608,7 @@ class App(Generic[ReturnType], DOMNode):
         self._exit_renderables.clear()
 
     async def process_messages(self) -> None:
-        active_app.set(self)
+        self._set_active()
         log("---")
         log(f"driver={self.driver_class}")
 
@@ -835,7 +854,7 @@ class App(Generic[ReturnType], DOMNode):
         if isinstance(event, events.Mount):
             screen = Screen()
             self.register(self, screen)
-            await self.push_screen(screen)
+            self.push_screen(screen)
             await super().on_event(event)
 
         elif isinstance(event, events.InputEvent) and not event.is_forwarded:
@@ -876,12 +895,18 @@ class App(Generic[ReturnType], DOMNode):
             action_target = default_namespace or self
             action_name = target
 
-        log("ACTION", action_target, action_name)
+        log("action", action)
         await self.dispatch_action(action_target, action_name, params)
 
     async def dispatch_action(
         self, namespace: object, action_name: str, params: Any
     ) -> None:
+        log(
+            "dispatch_action",
+            namespace=namespace,
+            action_name=action_name,
+            params=params,
+        )
         _rich_traceback_guard = True
         method_name = f"action_{action_name}"
         method = getattr(namespace, method_name, None)
diff --git a/src/textual/css/model.py b/src/textual/css/model.py
index 15459657e..37367fd7e 100644
--- a/src/textual/css/model.py
+++ b/src/textual/css/model.py
@@ -83,7 +83,7 @@ class Selector:
         return self._checks[self.type](node)
 
     def _check_universal(self, node: DOMNode) -> bool:
-        return True
+        return node.has_pseudo_class(*self.pseudo_classes)
 
     def _check_type(self, node: DOMNode) -> bool:
         if node.css_type != self._name_lower:
diff --git a/src/textual/dom.py b/src/textual/dom.py
index c906ea78b..874ef2a6e 100644
--- a/src/textual/dom.py
+++ b/src/textual/dom.py
@@ -439,8 +439,11 @@ class DOMNode(MessagePump):
 
         """
         self._classes.update(class_names)
-        self.app.stylesheet.update(self.app, animate=True)
-        self.refresh()
+        try:
+            self.app.stylesheet.update(self.app, animate=True)
+            self.refresh()
+        except LookupError:
+            pass
 
     def remove_class(self, *class_names: str) -> None:
         """Remove class names from this Node.
@@ -450,8 +453,11 @@ class DOMNode(MessagePump):
 
         """
         self._classes.difference_update(class_names)
-        self.app.stylesheet.update(self.app, animate=True)
-        self.refresh()
+        try:
+            self.app.stylesheet.update(self.app, animate=True)
+            self.refresh()
+        except LookupError:
+            pass
 
     def toggle_class(self, *class_names: str) -> None:
         """Toggle class names on this Node.
@@ -461,8 +467,11 @@ class DOMNode(MessagePump):
 
         """
         self._classes.symmetric_difference_update(class_names)
-        self.app.stylesheet.update(self.app, animate=True)
-        self.refresh()
+        try:
+            self.app.stylesheet.update(self.app, animate=True)
+            self.refresh()
+        except LookupError:
+            pass
 
     def has_pseudo_class(self, *class_names: str) -> bool:
         """Check for pseudo class (such as hover, focus etc)"""
diff --git a/src/textual/message_pump.py b/src/textual/message_pump.py
index ac217bb85..4da07f2c8 100644
--- a/src/textual/message_pump.py
+++ b/src/textual/message_pump.py
@@ -240,7 +240,7 @@ class MessagePump:
             except CancelledError:
                 raise
             except Exception as error:
-                self.app.panic(error)
+                self.app.on_exception(error)
                 break
             finally:
                 if self._message_queue.empty():
diff --git a/src/textual/screen.py b/src/textual/screen.py
index 1074f87f0..75607ab44 100644
--- a/src/textual/screen.py
+++ b/src/textual/screen.py
@@ -160,9 +160,9 @@ class Screen(Widget):
             else:
                 widget, region = self.get_widget_at(event.x, event.y)
         except errors.NoWidget:
-            await self.app.set_mouse_over(None)
+            await self.app._set_mouse_over(None)
         else:
-            await self.app.set_mouse_over(widget)
+            await self.app._set_mouse_over(widget)
             mouse_event = events.MouseMove(
                 self,
                 event.x - region.x,
diff --git a/src/textual/widget.py b/src/textual/widget.py
index 28ab5ad67..1630537ac 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -529,7 +529,7 @@ class Widget(DOMNode):
         Returns:
             bool: True if this widget is a container.
         """
-        return self.styles.layout is not None
+        return self.styles.layout is not None or bool(self.children)
 
     def watch_mouse_over(self, value: bool) -> None:
         """Update from CSS if mouse over state changes."""
diff --git a/src/textual/widgets/_button.py b/src/textual/widgets/_button.py
index 71e69c76c..46e8039dd 100644
--- a/src/textual/widgets/_button.py
+++ b/src/textual/widgets/_button.py
@@ -36,8 +36,7 @@ class Button(Widget, can_focus=True):
     }
 
     App.-show-focus Button:focus {
-        tint: $accent 20%;
-        
+        tint: $accent 20%;        
     }
     
     """
@@ -80,7 +79,5 @@ class Button(Widget, can_focus=True):
             await self.emit(Button.Pressed(self))
 
     async def on_key(self, event: events.Key) -> None:
-        self.log("BUTTON KEY", event)
         if event.key == "enter" and not self.disabled:
-            self.log("PRESSEd")
             await self.emit(Button.Pressed(self))
diff --git a/tests/test_focus.py b/tests/test_focus.py
new file mode 100644
index 000000000..167738494
--- /dev/null
+++ b/tests/test_focus.py
@@ -0,0 +1,71 @@
+from textual.app import App
+from textual.screen import Screen
+from textual.widget import Widget
+
+
+class Focusable(Widget, can_focus=True):
+    pass
+
+
+class NonFocusable(Widget, can_focus=False):
+    pass
+
+
+def test_focus_chain():
+
+    app = App()
+    app.push_screen(Screen())
+
+    # Check empty focus chain
+    assert not app.focus_chain
+
+    app.screen.add_children(
+        Focusable(id="foo"),
+        NonFocusable(id="bar"),
+        Focusable(Focusable(id="Paul"), id="container1"),
+        NonFocusable(Focusable(id="Jessica"), id="container2"),
+        Focusable(id="baz"),
+    )
+
+    focused = [widget.id for widget in app.focus_chain]
+    assert focused == ["foo", "Paul", "baz"]
+
+
+def test_show_focus():
+    app = App()
+    app.push_screen(Screen())
+    app.screen.add_children(
+        Focusable(id="foo"),
+        NonFocusable(id="bar"),
+        Focusable(Focusable(id="Paul"), id="container1"),
+        NonFocusable(Focusable(id="Jessica"), id="container2"),
+        Focusable(id="baz"),
+    )
+
+    focused = [widget.id for widget in app.focus_chain]
+    assert focused == ["foo", "Paul", "baz"]
+
+    assert app.focused is None
+    assert not app.has_class("-show-focus")
+    app.show_focus()
+    assert app.has_class("-show-focus")
+
+
+def test_focus_next_and_previous():
+
+    app = App()
+    app.push_screen(Screen())
+    app.screen.add_children(
+        Focusable(id="foo"),
+        NonFocusable(id="bar"),
+        Focusable(Focusable(id="Paul"), id="container1"),
+        NonFocusable(Focusable(id="Jessica"), id="container2"),
+        Focusable(id="baz"),
+    )
+
+    assert app.focus_next().id == "foo"
+    assert app.focus_next().id == "Paul"
+    assert app.focus_next().id == "baz"
+
+    assert app.focus_previous().id == "Paul"
+    assert app.focus_previous().id == "foo"