fix(tree): fix expanded node styles

CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
-### Add
+### Added
 
 - Added `x_axis` and `y_axis` parameters to `Widget.scroll_to_region` https://github.com/Textualize/textual/pull/5047
 
@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fixed widgets occasionally not getting Resize events https://github.com/Textualize/textual/pull/5048
+- Fixed `Tree` expanded node styles https://github.com/Textualize/textual/issues/5050
 
 ## [0.80.1] - 2024-09-24
 

src/textual/widgets/_directory_tree.py

@@ -485,6 +485,7 @@ def _populate_node(self, node: TreeNode[DirEntry], content: Iterable[Path]) -> N
                 allow_expand=self._safe_is_dir(path),
             )
         node.expand()
+        self.move_cursor(node)
 
     def _directory_content(self, location: Path, worker: Worker) -> Iterator[Path]:
         """Load the content of a given directory.

src/textual/widgets/_tree.py

@@ -654,7 +654,7 @@ class Tree(Generic[TreeDataType], ScrollView, can_focus=True):
     """Show the root of the tree."""
     hover_line = var(-1)
     """The line number under the mouse pointer, or -1 if not under the mouse pointer."""
-    cursor_line = var(-1)
+    cursor_line = var(-1, always_update=True)
     """The line with the cursor, or -1 if no cursor."""
     show_guides = reactive(True)
     """Enable display of tree guide lines."""
@@ -846,7 +846,7 @@ def render_label(
 
         if node._allow_expand:
             prefix = (
-                self.ICON_NODE if node.is_expanded else self.ICON_NODE_EXPANDED,
+                self.ICON_NODE_EXPANDED if node.is_expanded else self.ICON_NODE,
                 base_style + TOGGLE_STYLE,
             )
         else: