Textualize
diff --git a/‎CHANGELOG.md‎
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diff --git a/‎docs/widgets/text_area.md‎
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diff --git a/‎src/textual/_text_area_theme.py‎
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@@ -16,7 +16,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
-- Renamed `TextArea.tab_behaviour` to `TextArea.tab_behavior` https://github.com/Textualize/textual/pull/4124
+- Breaking change: Renamed `TextArea.tab_behaviour` to `TextArea.tab_behavior` https://github.com/Textualize/textual/pull/4124
+- `TextArea.theme` now defaults to `"css"` instead of None, and is no longer optional https://github.com/Textualize/textual/pull/4157
 
 ## [0.50.1] - 2024-02-09
 
 
@@ -1,7 +1,6 @@
-
 # TextArea
 
-!!! tip 
+!!! tip
 
     Added in version 0.38.0. Soft wrapping added in version 0.48.0.
 
@@ -68,7 +67,6 @@ text_area.language = "markdown"
 !!! note
     More built-in languages will be added in the future. For now, you can [add your own](#adding-support-for-custom-languages).
 
-
 ### Reading content from `TextArea`
 
 There are a number of ways to retrieve content from the `TextArea`:
@@ -136,7 +134,7 @@ There are a number of additional utility methods available for interacting with
 
 ##### Location information
 
-A number of properties exist on `TextArea` which give information about the current cursor location.
+Many properties exist on `TextArea` which give information about the current cursor location.
 These properties begin with `cursor_at_`, and return booleans.
 For example, [`cursor_at_start_of_line`][textual.widgets._text_area.TextArea.cursor_at_start_of_line] tells us if the cursor is at a start of line.
 
@@ -175,12 +173,14 @@ the cursor, selection, gutter, and more.
 
 #### Default theme
 
-The default `TextArea` theme is called `css`.
-This a theme which takes values entirely from CSS.
+The default `TextArea` theme is called `css`, which takes it's values entirely from CSS.
 This means that the default appearance of the widget fits nicely into a standard Textual application,
 and looks right on both dark and light mode.
 
-More complex applications such as code editors will likely want to use pre-defined themes such as `monokai`.
+When using the `css` theme, you can make use of [component classes][textual.widgets.TextArea.COMPONENT_CLASSES] to style elements of the `TextArea`.
+For example, the CSS code `TextArea .text-area--cursor { background: green; }` will make the cursor `green`.
+
+More complex applications such as code editors may want to use pre-defined themes such as `monokai`.
 This involves using a `TextAreaTheme` object, which we cover in detail below.
 This allows full customization of the `TextArea`, including syntax highlighting, at the code level.
 
@@ -190,15 +190,15 @@ The initial theme of the `TextArea` is determined by the `theme` parameter.
 
 ```python
 # Create a TextArea with the 'dracula' theme.
-yield TextArea("print(123)", language="python", theme="dracula")
+yield TextArea.code_editor("print(123)", language="python", theme="dracula")
 ```
 
 You can check which themes are available using the [`available_themes`][textual.widgets._text_area.TextArea.available_themes] property.
 
 ```python
 >>> text_area = TextArea()
 >>> print(text_area.available_themes)
-{'dracula', 'github_light', 'monokai', 'vscode_dark'}
+{'css', 'dracula', 'github_light', 'monokai', 'vscode_dark'}
 ```
 
 After creating a `TextArea`, you can change the theme by setting the [`theme`][textual.widgets._text_area.TextArea.theme]
@@ -212,7 +212,12 @@ On setting this attribute the `TextArea` will immediately refresh to display the
 
 #### Custom themes
 
-Using custom (non-builtin) themes is two-step process:
+!!! note
+
+    Custom themes are only relevant for people who are looking to customize syntax highlighting.
+    If you're only editing plain text, and wish to recolor aspects of the `TextArea`, you should use the [provided component classes][textual.widgets.TextArea.COMPONENT_CLASSES].
+
+Using custom (non-builtin) themes is a two-step process:
 
 1. Create an instance of [`TextAreaTheme`][textual.widgets.text_area.TextAreaTheme].
 2. Register it using [`TextArea.register_theme`][textual.widgets._text_area.TextArea.register_theme].
@@ -297,6 +302,27 @@ The character(s) inserted when you press tab is controlled by setting the `inden
 
 If `indent_type == "spaces"`, pressing ++tab++ will insert up to `indent_width` spaces in order to align with the next tab stop.
 
+### Undo and redo
+
+`TextArea` offers `undo` and `redo` methods.
+By default, `undo` is bound to <kbd>Ctrl</kbd>+<kbd>Z</kbd> and `redo` to <kbd>Ctrl</kbd>+<kbd>Y</kbd>.
+
+The `TextArea` uses a heuristic to place _checkpoints_ after certain types of edit.
+When you call `undo`, all of the edits between now and the most recent checkpoint are reverted.
+You can manually add a checkpoint by calling the [`TextArea.history.checkpoint()`][textual.widgets.text_area.EditHistory.checkpoint] instance method.
+
+The undo and redo history uses a stack-based system, where a single item on the stack represents a single checkpoint.
+In memory-constrained environments, you may wish to reduce the maximum number of checkpoints that can exist.
+You can do this by passing the `max_checkpoints` argument to the `TextArea` constructor.
+
+### Read-only mode
+
+`TextArea.read_only` is a boolean reactive attribute which, if `True`, will prevent users from modifying content in the `TextArea`.
+
+While `read_only=True`, you can still modify the content programmatically.
+
+While this mode is active, the `TextArea` receives the `-read-only` CSS class, which you can use to supply custom styles for read-only mode.
+
 ### Line separators
 
 When content is loaded into `TextArea`, the content is scanned from beginning to end
@@ -459,7 +485,6 @@ If you notice some highlights are missing after registering a language, the issu
     The names assigned in tree-sitter highlight queries are often reused across multiple languages.
     For example, `@string` is used in many languages to highlight strings.
 
-
 #### Navigation and wrapping information
 
 If you're building functionality on top of `TextArea`, it may be useful to inspect the `navigator` and `wrapped_document` attributes.
@@ -473,14 +498,15 @@ A detailed view of these classes is out of scope, but do note that a lot of the
 
 | Name                   | Type                     | Default       | Description                                                      |
 |------------------------|--------------------------|---------------|------------------------------------------------------------------|
-| `language`             | `str | None`         | `None`                                                           | The language to use for syntax highlighting.     |
-| `theme`                | `str | None`         | `TextAreaTheme.default()`                                        | The theme to use for syntax highlighting.         |
+| `language`             | `str | None`             | `None`        | The language to use for syntax highlighting.                     |
+| `theme`                | `str`                    | `"css"`       | The theme to use.                                                |
 | `selection`            | `Selection`              | `Selection()` | The current selection.                                           |
 | `show_line_numbers`    | `bool`                   | `False`       | Show or hide line numbers.                                       |
 | `indent_width`         | `int`                    | `4`           | The number of spaces to indent and width of tabs.                |
 | `match_cursor_bracket` | `bool`                   | `True`        | Enable/disable highlighting matching brackets under cursor.      |
 | `cursor_blink`         | `bool`                   | `True`        | Enable/disable blinking of the cursor when the widget has focus. |
 | `soft_wrap`            | `bool`                   | `True`        | Enable/disable soft wrapping.                                    |
+| `read_only`            | `bool`                   | `False`       | Enable/disable read-only mode.                                   |
 
 ## Messages
 
@@ -496,7 +522,6 @@ The `TextArea` widget defines the following bindings:
       show_root_heading: false
       show_root_toc_entry: false
 
-
 ## Component classes
 
 The `TextArea` defines component classes that can style various aspects of the widget.
@@ -513,11 +538,11 @@ Styles from the `theme` attribute take priority.
 - [`TextAreaTheme`][textual.widgets.text_area.TextAreaTheme] - theming the `TextArea`
 - [`DocumentNavigator`][textual.widgets.text_area.DocumentNavigator] - guides cursor movement 
 - [`WrappedDocument`][textual.widgets.text_area.WrappedDocument] - manages wrapping the document 
+- [`EditHistory`][textual.widgets.text_area.EditHistory] - manages the undo stack
 - The tree-sitter documentation [website](https://tree-sitter.github.io/tree-sitter/).
 - The tree-sitter Python bindings [repository](https://github.com/tree-sitter/py-tree-sitter).
 - `py-tree-sitter-languages` [repository](https://github.com/grantjenks/py-tree-sitter-languages) (provides binary wheels for a large variety of tree-sitter languages).
 
-
 ## Additional notes
 
 - To remove the outline effect when the `TextArea` is focused, you can set `border: none; padding: 0;` in your CSS.
 
@@ -119,9 +119,6 @@ def apply_css(self, text_area: TextArea) -> None:
         if self.cursor_line_gutter_style is None:
             self.cursor_line_gutter_style = get_style("text-area--cursor-gutter")
 
-        if self.cursor_line_gutter_style is None and self.cursor_line_style is not None:
-            self.cursor_line_gutter_style = self.cursor_line_style.copy()
-
         if self.bracket_matching_style is None:
             matching_bracket_style = get_style("text-area--matching-bracket")
             if matching_bracket_style:
@@ -182,15 +179,6 @@ def builtin_themes(cls) -> list[TextAreaTheme]:
         """
         return list(_BUILTIN_THEMES.values())
 
-    @classmethod
-    def default(cls) -> TextAreaTheme:
-        """Get the default syntax theme.
-
-        Returns:
-            The default TextAreaTheme (probably "css").
-        """
-        return _CSS_THEME
-
 
 _MONOKAI = TextAreaTheme(
     name="monokai",
@@ -388,6 +376,3 @@ def default(cls) -> TextAreaTheme:
     "vscode_dark": _DARK_VS,
     "github_light": _GITHUB_LIGHT,
 }
-
-DEFAULT_THEME = TextAreaTheme.get_builtin_theme("basic")
-"""The default TextAreaTheme used by Textual."""