optimize styles cache render

src/textual/_styles_cache.py

@@ -63,6 +63,8 @@ def __init__(self) -> None:
         self._cache: dict[int, Strip] = {}
         self._dirty_lines: set[int] = set()
         self._width = 1
+        self._simple_strip: Strip | None = None
+        """A simple strip consisting of left border + background + right border, which may be reused in a render."""
 
     def __rich_repr__(self) -> rich.repr.Result:
         if self._dirty_lines:
@@ -106,6 +108,7 @@ def render_widget(self, widget: Widget, crop: Region) -> list[Strip]:
         """
         border_title = widget._border_title
         border_subtitle = widget._border_subtitle
+        self._simple_strip = None
 
         base_background, background = widget.background_colors
         styles = widget.styles
@@ -348,6 +351,7 @@ def post(segments: Iterable[Segment]) -> Iterable[Segment]:
                 segments = _apply_opacity(segments, base_background, opacity)
             return segments
 
+        cache_simple_strip: bool = False
         line: Iterable[Segment]
         # Draw top or bottom borders (A)
         if (border_top and y == 0) or (border_bottom and y == height - 1):
@@ -411,11 +415,13 @@ def post(segments: Iterable[Segment]) -> Iterable[Segment]:
                 label_segments,
                 label_alignment,  # type: ignore
             )
-
         # Draw padding (B)
         elif (pad_top and y < gutter.top) or (
             pad_bottom and y >= height - gutter.bottom
         ):
+            if self._simple_strip is not None:
+                return self._simple_strip
+            cache_simple_strip = True
             background_rich_style = inner.rich_style
             left_style = Style(
                 foreground=base_background + border_left_color.multiply_alpha(opacity)
@@ -498,6 +504,7 @@ def post(segments: Iterable[Segment]) -> Iterable[Segment]:
                 line = [left, *line]
             else:
                 line = [*line, right]
-
         strip = Strip(post(line), width)
+        if cache_simple_strip:
+            self._simple_strip = strip
         return strip

src/textual/widgets/_collapsible.py

@@ -17,6 +17,8 @@
 class CollapsibleTitle(Static, can_focus=True):
     """Title and symbol for the Collapsible."""
 
+    BINDING_GROUP_TITLE = "Collapsible"
+
     ALLOW_SELECT = False
     DEFAULT_CSS = """
     CollapsibleTitle {

src/textual/widgets/_help_panel.py

@@ -96,7 +96,11 @@ def update_help(self, focused_widget: Widget | None) -> None:
             return
         self.set_class(focused_widget is not None, "-show-help")
         if focused_widget is not None:
-            help = focused_widget.HELP or ""
+            help: str = ""
+            for node in focused_widget.ancestors_with_self:
+                if isinstance(node, Widget) and node.HELP:
+                    help = node.HELP
+                    break
             if not help:
                 self.remove_class("-show-help")
             try:

src/textual/widgets/_input.py

@@ -71,6 +71,7 @@ def is_empty(self) -> bool:
 class Input(ScrollView):
     """A text input widget."""
 
+    BINDING_GROUP_TITLE = "Input"
     BINDINGS: ClassVar[list[BindingType]] = [
         Binding("left", "cursor_left", "Move cursor left", show=False),
         Binding(