diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index e4369ce2e..b65350ed6 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -2,11 +2,12 @@
 # See https://pre-commit.com/hooks.html for more hooks
 repos:
 -   repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v3.2.0
+    rev: v4.3.0
     hooks:
     -   id: trailing-whitespace
     -   id: end-of-file-fixer
     -   id: check-yaml
+        args: ['--unsafe']
 -   repo: https://github.com/psf/black
     rev: 22.3.0
     hooks:
diff --git a/docs/examples/styles/content_align.css b/docs/examples/styles/content_align.css
new file mode 100644
index 000000000..7024809b0
--- /dev/null
+++ b/docs/examples/styles/content_align.css
@@ -0,0 +1,20 @@
+#box1 {
+    content-align: left top;
+    background: red;
+}
+
+#box2 {
+    content-align: center middle;
+    background: green;
+}
+
+#box3 {
+    content-align: right bottom;
+    background: blue;
+}
+
+Static {
+    height: 1fr;
+    padding: 1;
+    color: white;
+}
diff --git a/docs/examples/styles/content_align.py b/docs/examples/styles/content_align.py
new file mode 100644
index 000000000..930553f40
--- /dev/null
+++ b/docs/examples/styles/content_align.py
@@ -0,0 +1,13 @@
+from textual.app import App
+from textual.widgets import Static
+
+
+class ContentAlignApp(App):
+    def compose(self):
+        yield Static("With [i]content-align[/] you can...", id="box1")
+        yield Static("...[b]Easily align content[/]...", id="box2")
+        yield Static("...Horizontally [i]and[/] vertically!", id="box3")
+
+
+app = ContentAlignApp(css_path="content_align.css")
+app.run()
diff --git a/docs/examples/styles/scrollbar_gutter.css b/docs/examples/styles/scrollbar_gutter.css
new file mode 100644
index 000000000..ed62eb852
--- /dev/null
+++ b/docs/examples/styles/scrollbar_gutter.css
@@ -0,0 +1,8 @@
+Screen {
+    scrollbar-gutter: stable;
+}
+
+#text-box {
+    color: floralwhite;
+    background: darkmagenta;
+}
diff --git a/docs/examples/styles/scrollbar_gutter.py b/docs/examples/styles/scrollbar_gutter.py
new file mode 100644
index 000000000..b847b3434
--- /dev/null
+++ b/docs/examples/styles/scrollbar_gutter.py
@@ -0,0 +1,18 @@
+from textual.app import App
+from textual.widgets import Static
+
+TEXT = """I must not fear.
+Fear is the mind-killer.
+Fear is the little-death that brings total obliteration.
+I will face my fear.
+I will permit it to pass over me and through me.
+And when it has gone past, I will turn the inner eye to see its path.
+Where the fear has gone there will be nothing. Only I will remain."""
+
+
+class ScrollbarGutterApp(App):
+    def compose(self):
+        yield Static(TEXT, id="text-box")
+
+
+app = ScrollbarGutterApp(css_path="scrollbar_gutter.css")
diff --git a/docs/styles/border.md b/docs/styles/border.md
index 3ac9a119a..c060bfb25 100644
--- a/docs/styles/border.md
+++ b/docs/styles/border.md
@@ -3,7 +3,7 @@
 The `border` rule enables the drawing of a box around a widget. A border is set with a border value (see below) followed by a color.
 
 | Border value | Explanation                                             |
-| ------------ | ------------------------------------------------------- |
+| ------------ |---------------------------------------------------------|
 | `"ascii"`    | A border with plus, hyphen, and vertical bar            |
 | `"blank"`    | A blank border (reserves space for a border)            |
 | `"dashed"`   | Dashed line border                                      |
diff --git a/docs/styles/content_align.md b/docs/styles/content_align.md
new file mode 100644
index 000000000..72ec6d132
--- /dev/null
+++ b/docs/styles/content_align.md
@@ -0,0 +1,65 @@
+# Content-align
+
+The `content-align` property allows you to align content _inside_ a widget.
+
+You can specify the alignment of content on both the horizontal and vertical axes.
+
+## Syntax
+
+```
+content-align: <HORIZONTAL> <VERTICAL>;
+```
+
+### Values
+
+#### `HORIZONTAL`
+
+| Value            | Description                                        |
+|------------------|----------------------------------------------------|
+| `left` (default) | Align content on the left of the horizontal axis   |
+| `center`         | Align content in the center of the horizontal axis |
+| `right`          | Align content on the right of the horizontal axis  |
+
+#### `VERTICAL`
+
+| Value           | Description                                      |
+|-----------------|--------------------------------------------------|
+| `top` (default) | Align content at the top of the vertical axis    |
+| `middle`        | Align content in the middle of the vertical axis |
+| `bottom`        | Align content at the bottom of the vertical axis |
+
+## Example
+
+=== "content_align.py"
+
+    ```python
+    --8<-- "docs/examples/styles/content_align.py"
+    ```
+
+=== "content_align.css"
+
+    ```scss
+    --8<-- "docs/examples/styles/content_align.css"
+    ```
+
+=== "Output"
+
+    ```{.textual path="docs/examples/styles/content_align.py"}
+    ```
+
+## CSS
+
+```sass
+/* Align content in the very center of a widget */
+content-align: center middle;
+/* Align content at the top right of a widget */
+content-align: right top;
+```
+
+## Python
+```python
+# Align content in the very center of a widget
+widget.styles.content_align = ("center", "middle")
+# Align content at the top right of a widget
+widget.styles.content_align = ("right", "top")
+```
diff --git a/docs/styles/scrollbar_gutter.md b/docs/styles/scrollbar_gutter.md
new file mode 100644
index 000000000..7c2ed5e44
--- /dev/null
+++ b/docs/styles/scrollbar_gutter.md
@@ -0,0 +1,53 @@
+# Scrollbar-gutter
+
+The `scrollbar-gutter` rule allows authors to reserve space for the vertical scrollbar.
+
+Setting the value to `stable` prevents unwanted layout changes when the scrollbar becomes visible.
+
+## Syntax
+
+```
+scrollbar-gutter: [auto|stable];
+```
+
+### Values
+
+| Value            | Description                                      |
+|------------------|--------------------------------------------------|
+| `auto` (default) | No space is reserved for the vertical scrollbar. |
+| `stable`         | Space is reserved for the vertical scrollbar.    |
+
+## Example
+
+In the example below, notice the gap reserved for the scrollbar on the right side of the
+terminal window.
+
+=== "scrollbar_gutter.py"
+
+    ```python
+    --8<-- "docs/examples/styles/scrollbar_gutter.py"
+    ```
+
+=== "scrollbar_gutter.css"
+
+    ```scss
+    --8<-- "docs/examples/styles/scrollbar_gutter.css"
+    ```
+
+=== "Output"
+
+    ```{.textual path="docs/examples/styles/scrollbar_gutter.py"}
+    ```
+
+## CSS
+
+```sass
+/* Reserve space for vertical scrollbar */
+scrollbar-gutter: stable;
+```
+
+## Python
+
+```python
+self.styles.scrollbar_gutter = "stable"
+```
diff --git a/mkdocs.yml b/mkdocs.yml
index fa0fdc5d8..f6c520f31 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -36,12 +36,13 @@ nav:
     - "events/resize.md"
     - "events/screen_resume.md"
     - "events/screen_suspend.md"
-    - "events/show.md"
-  - Styles:    
+    - "events/show.md"  
+  - Styles:
     - "styles/background.md"
     - "styles/border.md"
     - "styles/box_sizing.md"
     - "styles/color.md"
+    - "styles/content_align.md"
     - "styles/display.md"
     - "styles/min_height.md"
     - "styles/max_height.md"
@@ -55,6 +56,7 @@ nav:
     - "styles/padding.md"
     - "styles/scrollbar.md"
     - "styles/scrollbar_size.md"
+    - "styles/scrollbar_gutter.md"
     - "styles/text_style.md"
     - "styles/tint.md"
     - "styles/visibility.md"
@@ -87,7 +89,7 @@ markdown_extensions:
   - pymdownx.superfences
   - pymdownx.snippets
   - pymdownx.tabbed:
-      alternate_style: true 
+      alternate_style: true
   - pymdownx.snippets
   - markdown.extensions.attr_list
 
diff --git a/sandbox/darren/just_a_box.py b/sandbox/darren/just_a_box.py
index 781c66f67..ee8be631e 100644
--- a/sandbox/darren/just_a_box.py
+++ b/sandbox/darren/just_a_box.py
@@ -1,11 +1,11 @@
 from __future__ import annotations
 
+import asyncio
+
 from rich.console import RenderableType
-from rich.panel import Panel
 
 from textual import events
 from textual.app import App, ComposeResult
-from textual.layout import Horizontal, Vertical
 from textual.widget import Widget
 
 
@@ -18,37 +18,22 @@ class Box(Widget, can_focus=True):
         super().__init__(*children, id=id, classes=classes)
 
     def render(self) -> RenderableType:
-        return Panel("Box")
+        return "Box"
 
 
 class JustABox(App):
     def compose(self) -> ComposeResult:
-        yield Horizontal(
-            Vertical(
-                Box(id="box1", classes="box"),
-                Box(id="box2", classes="box"),
-                # Box(id="box3", classes="box"),
-                # Box(id="box4", classes="box"),
-                # Box(id="box5", classes="box"),
-                # Box(id="box6", classes="box"),
-                # Box(id="box7", classes="box"),
-                # Box(id="box8", classes="box"),
-                # Box(id="box9", classes="box"),
-                # Box(id="box10", classes="box"),
-                id="left_pane",
-            ),
-            Box(id="middle_pane"),
-            Vertical(
-                Box(id="boxa", classes="box"),
-                Box(id="boxb", classes="box"),
-                Box(id="boxc", classes="box"),
-                id="right_pane",
-            ),
-            id="horizontal",
-        )
+        self.box = Box()
+        yield self.box
 
-    def key_p(self):
-        print(self.query("#horizontal").first().styles.layout)
+    def key_a(self):
+        self.animator.animate(
+            self.box.styles,
+            "opacity",
+            value=0.0,
+            duration=2.0,
+            on_complete=self.box.remove,
+        )
 
     async def on_key(self, event: events.Key) -> None:
         await self.dispatch_key(event)
diff --git a/src/textual/_animator.py b/src/textual/_animator.py
index dbc5d9670..198c0e266 100644
--- a/src/textual/_animator.py
+++ b/src/textual/_animator.py
@@ -8,9 +8,10 @@ from typing import Any, Callable, TypeVar
 from dataclasses import dataclass
 
 from . import _clock
+from ._callback import invoke
 from ._easing import DEFAULT_EASING, EASING
 from ._timer import Timer
-from ._types import MessageTarget
+from ._types import MessageTarget, CallbackType
 
 if sys.version_info >= (3, 8):
     from typing import Protocol, runtime_checkable
@@ -30,8 +31,20 @@ class Animatable(Protocol):
 
 
 class Animation(ABC):
+
+    on_complete: CallbackType | None = None
+    """Callback to run after animation completes"""
+
     @abstractmethod
     def __call__(self, time: float) -> bool:  # pragma: no cover
+        """Call the animation, return a boolean indicating whether animation is in-progress or complete.
+
+        Args:
+            time (float): The current timestamp
+
+        Returns:
+            bool: True if the animation has finished, otherwise False.
+        """
         raise NotImplementedError("")
 
     def __eq__(self, other: object) -> bool:
@@ -48,6 +61,7 @@ class SimpleAnimation(Animation):
     end_value: float | Animatable
     final_value: object
     easing: EasingFunction
+    on_complete: CallbackType | None = None
 
     def __call__(self, time: float) -> bool:
 
@@ -109,6 +123,7 @@ class BoundAnimator:
         duration: float | None = None,
         speed: float | None = None,
         easing: EasingFunction | str = DEFAULT_EASING,
+        on_complete: CallbackType | None = None,
     ) -> None:
         easing_function = EASING[easing] if isinstance(easing, str) else easing
         return self._animator.animate(
@@ -119,6 +134,7 @@ class BoundAnimator:
             duration=duration,
             speed=speed,
             easing=easing_function,
+            on_complete=on_complete,
         )
 
 
@@ -163,6 +179,7 @@ class Animator:
         duration: float | None = None,
         speed: float | None = None,
         easing: EasingFunction | str = DEFAULT_EASING,
+        on_complete: CallbackType | None = None,
     ) -> None:
         """Animate an attribute to a new value.
 
@@ -201,6 +218,7 @@ class Animator:
                 duration=duration,
                 speed=speed,
                 easing=easing_function,
+                on_complete=on_complete,
             )
         if animation is None:
             start_value = getattr(obj, attribute)
@@ -223,6 +241,7 @@ class Animator:
                 end_value=value,
                 final_value=final_value,
                 easing=easing_function,
+                on_complete=on_complete,
             )
         assert animation is not None, "animation expected to be non-None"
 
@@ -233,7 +252,7 @@ class Animator:
         self._animations[animation_key] = animation
         self._timer.resume()
 
-    def __call__(self) -> None:
+    async def __call__(self) -> None:
         if not self._animations:
             self._timer.pause()
         else:
@@ -241,7 +260,11 @@ class Animator:
             animation_keys = list(self._animations.keys())
             for animation_key in animation_keys:
                 animation = self._animations[animation_key]
-                if animation(animation_time):
+                animation_complete = animation(animation_time)
+                if animation_complete:
+                    completion_callback = animation.on_complete
+                    if completion_callback is not None:
+                        await invoke(completion_callback)
                     del self._animations[animation_key]
 
     def _get_time(self) -> float:
diff --git a/src/textual/_types.py b/src/textual/_types.py
index 180d02be4..7158e31a4 100644
--- a/src/textual/_types.py
+++ b/src/textual/_types.py
@@ -1,5 +1,6 @@
 import sys
-from typing import Awaitable, Callable, List, Optional, TYPE_CHECKING
+from typing import Awaitable, Callable, List, TYPE_CHECKING, Union
+
 from rich.segment import Segment
 
 if sys.version_info >= (3, 8):
@@ -11,8 +12,6 @@ else:
 if TYPE_CHECKING:
     from .message import Message
 
-Callback = Callable[[], None]
-
 
 class MessageTarget(Protocol):
     async def post_message(self, message: "Message") -> bool:
@@ -34,5 +33,5 @@ class EventTarget(Protocol):
 
 
 MessageHandler = Callable[["Message"], Awaitable]
-
 Lines = List[List[Segment]]
+CallbackType = Union[Callable[[], Awaitable[None]], Callable[[], None]]
diff --git a/src/textual/css/scalar_animation.py b/src/textual/css/scalar_animation.py
index ae37249f9..aa81ec805 100644
--- a/src/textual/css/scalar_animation.py
+++ b/src/textual/css/scalar_animation.py
@@ -1,8 +1,8 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Callable
 
-from .. import events, log
+from .._types import CallbackType
 from ..geometry import Offset
 from .._animator import Animation
 from .scalar import ScalarOffset
@@ -25,6 +25,7 @@ class ScalarAnimation(Animation):
         duration: float | None,
         speed: float | None,
         easing: EasingFunction,
+        on_complete: CallbackType | None = None,
     ):
         assert (
             speed is not None or duration is not None
@@ -35,6 +36,7 @@ class ScalarAnimation(Animation):
         self.attribute = attribute
         self.final_value = value
         self.easing = easing
+        self.on_complete = on_complete
 
         size = widget.outer_size
         viewport = widget.app.size
@@ -55,7 +57,6 @@ class ScalarAnimation(Animation):
         eased_factor = self.easing(factor)
 
         if eased_factor >= 1:
-            offset = self.final_value
             setattr(self.styles, self.attribute, self.final_value)
             return True
 
diff --git a/src/textual/css/styles.py b/src/textual/css/styles.py
index dd0b53e6f..c4e952ed3 100644
--- a/src/textual/css/styles.py
+++ b/src/textual/css/styles.py
@@ -10,6 +10,7 @@ from typing import TYPE_CHECKING, Any, Iterable, NamedTuple, cast
 import rich.repr
 from rich.style import Style
 
+from textual._types import CallbackType
 from .._animator import Animation, EasingFunction
 from ..color import Color
 from ..geometry import Offset, Spacing
@@ -579,9 +580,9 @@ class Styles(StylesBase):
         duration: float | None,
         speed: float | None,
         easing: EasingFunction,
+        on_complete: CallbackType | None = None,
     ) -> Animation | None:
-        from ..widget import Widget
-
+        # from ..widget import Widget
         # node = self.node
         # assert isinstance(self.node, Widget)
         if isinstance(value, ScalarOffset):
@@ -594,6 +595,7 @@ class Styles(StylesBase):
                 duration=duration,
                 speed=speed,
                 easing=easing,
+                on_complete=on_complete,
             )
         return None
 
@@ -760,7 +762,7 @@ class Styles(StylesBase):
             )
         elif has_rule("align_horizontal"):
             append_declaration("align-horizontal", self.align_horizontal)
-        elif has_rule("align_horizontal"):
+        elif has_rule("align_vertical"):
             append_declaration("align-vertical", self.align_vertical)
 
         if has_rule("content_align_horizontal") and has_rule("content_align_vertical"):
@@ -772,7 +774,7 @@ class Styles(StylesBase):
             append_declaration(
                 "content-align-horizontal", self.content_align_horizontal
             )
-        elif has_rule("content_align_horizontal"):
+        elif has_rule("content_align_vertical"):
             append_declaration("content-align-vertical", self.content_align_vertical)
 
         lines.sort()
diff --git a/src/textual/messages.py b/src/textual/messages.py
index 84bc8d14a..58e4cd2a6 100644
--- a/src/textual/messages.py
+++ b/src/textual/messages.py
@@ -1,8 +1,9 @@
 from __future__ import annotations
-from typing import TYPE_CHECKING, Callable, Awaitable, Union
+from typing import TYPE_CHECKING
 
 import rich.repr
 
+from ._types import CallbackType
 from .message import Message
 
 
@@ -11,9 +12,6 @@ if TYPE_CHECKING:
     from .widget import Widget
 
 
-CallbackType = Union[Callable[[], Awaitable[None]], Callable[[], None]]
-
-
 @rich.repr.auto
 class Update(Message, verbosity=3):
     def __init__(self, sender: MessagePump, widget: Widget):
diff --git a/src/textual/screen.py b/src/textual/screen.py
index f0b84b173..28f986a2d 100644
--- a/src/textual/screen.py
+++ b/src/textual/screen.py
@@ -12,8 +12,7 @@ from ._callback import invoke
 
 from .geometry import Offset, Region, Size
 from ._compositor import Compositor, MapGeometry
-from .messages import CallbackType
-from ._profile import timer
+from ._types import CallbackType
 from .reactive import Reactive
 from .renderables.blank import Blank
 from ._timer import Timer
diff --git a/tests/test_animator.py b/tests/test_animator.py
index fd3f7c038..926949b27 100644
--- a/tests/test_animator.py
+++ b/tests/test_animator.py
@@ -1,12 +1,10 @@
 from __future__ import annotations
 
-
 from dataclasses import dataclass
 from unittest.mock import Mock
 
 import pytest
 
-
 from textual._animator import Animator, SimpleAnimation
 from textual._easing import EASING, DEFAULT_EASING
 
@@ -184,8 +182,7 @@ class MockAnimator(Animator):
         return self._time
 
 
-def test_animator():
-
+async def test_animator():
     target = Mock()
     animator = MockAnimator(target)
     animate_test = AnimateTest()
@@ -206,11 +203,11 @@ def test_animator():
     assert animator._animations[(id(animate_test), "foo")] == expected
     assert not animator._on_animation_frame_called
 
-    animator()
+    await animator()
     assert animate_test.foo == 0
 
     animator._time = 5
-    animator()
+    await animator()
     assert animate_test.foo == 50
 
     # New animation in the middle of an existing one
@@ -218,12 +215,11 @@ def test_animator():
     assert animate_test.foo == 50
 
     animator._time = 6
-    animator()
+    await animator()
     assert animate_test.foo == 200
 
 
 def test_bound_animator():
-
     target = Mock()
     animator = MockAnimator(target)
     animate_test = AnimateTest()
@@ -245,3 +241,29 @@ def test_bound_animator():
         easing=EASING[DEFAULT_EASING],
     )
     assert animator._animations[(id(animate_test), "foo")] == expected
+
+
+def test_animator_on_complete_callback_not_fired_before_duration_ends():
+    callback = Mock()
+    animate_test = AnimateTest()
+    animator = MockAnimator(Mock())
+
+    animator.animate(animate_test, "foo", 200, duration=10, on_complete=callback)
+
+    animator._time = 9
+    animator()
+
+    assert not callback.called
+
+
+async def test_animator_on_complete_callback_fired_at_duration():
+    callback = Mock()
+    animate_test = AnimateTest()
+    animator = MockAnimator(Mock())
+
+    animator.animate(animate_test, "foo", 200, duration=10, on_complete=callback)
+
+    animator._time = 10
+    await animator()
+
+    callback.assert_called_once_with()