Add container 'Center'.

This container will centre children horizontally.

Related issues: #1957.

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 - Added `HorizontalScroll` https://github.com/Textualize/textual/issues/1957
+- Added `Center` https://github.com/Textualize/textual/issues/1957
 
 
 ## [0.14.0] - 2023-03-09

src/textual/containers.py

@@ -49,6 +49,18 @@ class HorizontalScroll(Widget):
     """
 
 
+class Center(Widget):
+    """A container widget which centers children horizontally."""
+
+    DEFAULT_CSS = """
+    Center {
+        align-horizontal: center;
+        width: 100%;
+        height: auto;
+    }
+    """
+
+
 class Grid(Widget):
     """A container widget with grid alignment."""
 

tests/test_containers.py

@@ -1,12 +1,12 @@
 """Test basic functioning of some containers."""
 
 from textual.app import App, ComposeResult
-from textual.containers import Horizontal, HorizontalScroll
+from textual.containers import Center, Horizontal, HorizontalScroll
 from textual.widgets import Label
 
 
 async def test_horizontal_vs_horizontalscroll_scrolling():
-    """Check the default scrollbar behaviours for Horizontal and HorizontalScroll."""
+    """Check the default scrollbar behaviours for `Horizontal` and `HorizontalScroll`."""
 
     class HorizontalsApp(App[None]):
         CSS = """
@@ -32,3 +32,18 @@ def compose(self) -> ComposeResult:
         assert horizontal.size.height == horizontal_scroll.size.height
         assert horizontal.scrollbars_enabled == (False, False)
         assert horizontal_scroll.scrollbars_enabled == (False, True)
+
+
+async def test_center_container():
+    """Check the size of the container `Center`."""
+
+    class CenterApp(App[None]):
+        def compose(self) -> ComposeResult:
+            with Center():
+                yield Label("<>\n<>\n<>")
+
+    app = CenterApp()
+    async with app.run_test():
+        center = app.query_one(Center)
+        assert center.size.width == app.size.width
+        assert center.size.height == 3