Fix focus after collapsible is expanded

CHANGELOG.md

@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fixed visual glitches and crash when changing `DataTable.header_height` https://github.com/Textualize/textual/pull/6128
 - Fixed TextArea.placeholder not handling multi-lines https://github.com/Textualize/textual/pull/6138
 - Fixed issue with RichLog when App.theme is set early https://github.com/Textualize/textual/pull/6141
+- Fixed children of collapsible not being focusable after collapsible is expanded https://github.com/Textualize/textual/pull/6143
 
 ## [6.1.0] - 2025-08-01
 

src/textual/css/_style_properties.py

@@ -841,6 +841,12 @@ def __set__(self, obj: StylesBase, value: EnumType | None = None):
                     children=self._refresh_children,
                     parent=self._refresh_parent,
                 )
+
+                if self._display:
+                    node = obj.node
+                    if node is not None and node.parent:
+                        node._nodes.updated()
+
         else:
             if value not in self._valid_values:
                 raise StyleValueError(

tests/snapshot_tests/test_snapshots.py

@@ -4675,3 +4675,18 @@ def on_ready(self) -> None:
             log_widget.write("Hello, World!")
 
     assert snap_compare(TestApp())
+
+
+def test_collapsible_focus_children(snap_compare) -> None:
+    """Regression test for https://github.com/Textualize/textual/issues/6140
+
+    You should see an expanded collapsible containing a button. The button should be focused.
+
+    """
+
+    class CollapseApp(App):
+        def compose(self) -> ComposeResult:
+            with Collapsible(title="Collapsible", collapsed=False):
+                yield Button("Hello")
+
+    assert snap_compare(CollapseApp(), press=["enter", "enter", "tab"])