background tint style (#5117)

* background tint style

* changelog

* hlines

* doc fix

* added tint

* missing snapshots

CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Fixed `RadioSet` not being scrollable https://github.com/Textualize/textual/issues/5100
 
+### Added
+
+- Added `background-tint` CSS rule https://github.com/Textualize/textual/pull/5117
+
 ## [0.83.0] - 2024-10-10
 
 ### Added

docs/examples/styles/background_tint.py

@@ -0,0 +1,24 @@
+from textual.app import App, ComposeResult
+from textual.containers import Vertical
+from textual.widgets import Label
+
+
+class BackgroundTintApp(App):
+    CSS_PATH = "background_tint.tcss"
+
+    def compose(self) -> ComposeResult:
+        with Vertical(id="tint1"):
+            yield Label("0%")
+        with Vertical(id="tint2"):
+            yield Label("25%")
+        with Vertical(id="tint3"):
+            yield Label("50%")
+        with Vertical(id="tint4"):
+            yield Label("75%")
+        with Vertical(id="tint5"):
+            yield Label("100%")
+
+
+if __name__ == "__main__":
+    app = BackgroundTintApp()
+    app.run()

docs/examples/styles/background_tint.tcss

@@ -0,0 +1,9 @@
+Vertical {
+    background: $panel;
+    color: auto 90%;
+}
+#tint1 { background-tint: $foreground 0%; }
+#tint2 { background-tint: $foreground 25%; }
+#tint3 { background-tint: $foreground 50%; }
+#tint4 { background-tint: $foreground 75% }
+#tint5 { background-tint: $foreground 100% }

docs/styles/background.md

@@ -90,4 +90,5 @@ widget.styles.background = Color(120, 60, 100)
 
 ## See also
 
+ - [`background-tint`](./background_tint.md) to blend a color with the background.
  - [`color`](./color.md) to set the color of text in a widget.

docs/styles/background_tint.md

@@ -0,0 +1,77 @@
+# Background-tint
+
+The `background-tint` style modifies the background color by tinting (blending) it with a new color.
+
+This style is typically used to subtly change the background of a widget for emphasis.
+For instance the following would make a focused widget have a slightly lighter background.
+
+```css
+MyWidget:focus {
+    background-tint: white 10%
+}
+```
+
+The background tint color should typically have less than 100% alpha, in order to modify the background color.
+If the alpha component is 100% then the tint color will replace the background color entirely.
+
+## Syntax
+
+--8<-- "docs/snippets/syntax_block_start.md"
+background-tint: <a href="../../css_types/color">&lt;color&gt;</a> [<a href="../../css_types/percentage">&lt;percentage&gt;</a>];
+--8<-- "docs/snippets/syntax_block_end.md"
+
+The `background-tint` style requires a [`<color>`](../css_types/color.md) optionally followed by [`<percentage>`](../css_types/percentage.md) to specify the color's opacity (clamped between `0%` and `100%`).
+
+## Examples
+
+### Basic usage
+
+This example shows background tint applied with alpha from 0 to 100%.
+
+=== "Output"
+
+    ```{.textual path="docs/examples/styles/background_tint.py"}
+    ```
+
+=== "background_tint.py"
+
+    ```python
+    --8<-- "docs/examples/styles/background_tint.py"
+    ```
+
+=== "background.tcss"
+
+    ```css hl_lines="5-9"
+    --8<-- "docs/examples/styles/background_tint.tcss"
+    ```
+
+
+## CSS
+
+```css
+/* 10% backgrouhnd tint */
+background-tint: blue 10%;
+
+
+/* 20% RGB color */
+background-tint: rgb(100, 120, 200, 0.2);
+
+```
+
+## Python
+
+You can use the same syntax as CSS, or explicitly set a `Color` object for finer-grained control.
+
+```python
+# Set 20% blue background tint
+widget.styles.background_tint = "blue 20%"
+
+from textual.color import Color
+# Set with a color object
+widget.styles.background_tint = Color(120, 60, 100, 0.5)
+```
+
+## See also
+
+ - [`background`](./background.md) to set the background color of a widget.
+ - [`color`](./color.md) to set the color of text in a widget.

mkdocs-nav.yml

@@ -75,6 +75,7 @@ nav:
           - "styles/index.md"
           - "styles/align.md"
           - "styles/background.md"
+          - "styles/background_tint.md"
           - "styles/border.md"
           - "styles/border_subtitle_align.md"
           - "styles/border_subtitle_background.md"

src/textual/css/_styles_builder.py

@@ -670,6 +670,7 @@ def process_color(self, name: str, tokens: list[Token]) -> None:
 
     process_tint = process_color
     process_background = process_color
+    process_background_tint = process_color
     process_scrollbar_color = process_color
     process_scrollbar_color_hover = process_color
     process_scrollbar_color_active = process_color

src/textual/css/styles.py

@@ -91,6 +91,8 @@ class RulesMap(TypedDict, total=False):
     background: Color
     text_style: Style
 
+    background_tint: Color
+
     opacity: float
     text_opacity: float
 
@@ -215,6 +217,7 @@ class StylesBase:
         "auto_color",
         "color",
         "background",
+        "background_tint",
         "opacity",
         "text_opacity",
         "tint",
@@ -285,6 +288,11 @@ class StylesBase:
     Supports `Color` objects but also strings e.g. "red" or "#ff0000"
     You can also specify an opacity after a color e.g. "blue 10%"
     """
+    background_tint = ColorProperty(Color(0, 0, 0, 0))
+    """Set a color to tint (blend) with the background.
+    Supports `Color` objects but also strings e.g. "red" or "#ff0000"
+    You can also specify an opacity after a color e.g. "blue 10%"   
+    """
     text_style = StyleFlagsProperty()
     """Set the text style of the widget using Rich StyleFlags.
     e.g. `"bold underline"` or `"b u strikethrough"`.
@@ -1011,6 +1019,8 @@ def append_declaration(name: str, value: str) -> None:
             append_declaration("color", self.color.hex)
         if "background" in rules:
             append_declaration("background", self.background.hex)
+        if "background_tint" in rules:
+            append_declaration("background-tint", self.background_tint.hex)
         if "text_style" in rules:
             append_declaration("text-style", str(get_rule("text_style")))
         if "tint" in rules:

src/textual/dom.py

@@ -1026,8 +1026,12 @@ def rich_style(self) -> Style:
             has_rule = styles.has_rule
             opacity *= styles.opacity
             if has_rule("background"):
-                text_background = background + styles.background
-                background += styles.background.multiply_alpha(opacity)
+                text_background = (
+                    background + styles.background + styles.background_tint
+                )
+                background += (
+                    styles.background + styles.background_tint
+                ).multiply_alpha(opacity)
             else:
                 text_background = background
             if has_rule("color"):
@@ -1115,7 +1119,7 @@ def background_colors(self) -> tuple[Color, Color]:
         for node in reversed(self.ancestors_with_self):
             styles = node.styles
             base_background = background
-            background += styles.background
+            background += styles.background + styles.background_tint
         return (base_background, background)
 
     @property
@@ -1131,7 +1135,9 @@ def _opacity_background_colors(self) -> tuple[Color, Color]:
             styles = node.styles
             base_background = background
             opacity *= styles.opacity
-            background += styles.background.multiply_alpha(opacity)
+            background += (styles.background + styles.background_tint).multiply_alpha(
+                opacity
+            )
         return (base_background, background)
 
     @property
@@ -1146,7 +1152,7 @@ def colors(self) -> tuple[Color, Color, Color, Color]:
         for node in reversed(self.ancestors_with_self):
             styles = node.styles
             base_background = background
-            background += styles.background
+            background += styles.background + styles.background_tint
             if styles.has_rule("color"):
                 base_color = color
                 if styles.auto_color: