Merge pull request #5890 from edward-jazzhands/fix_css_transparency

Fixed CSS transparency bug in _style_properties.py

Author: willmcgugan

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Fixed
+
+- Fixed issue with the "transparent" CSS value not being transparent when set using python
+
 ## [3.5.0] - 2025-06-20
 
 ### Changed

src/textual/css/_style_properties.py

@@ -991,7 +991,7 @@ def __set__(self, obj: StylesBase, color: Color | str | None) -> None:
                             self.name, context="inline", error=error, value=token
                         ),
                     )
-            parsed_color = parsed_color.with_alpha(alpha)
+            parsed_color = parsed_color.multiply_alpha(alpha)
 
             if obj.set_rule(self.name, parsed_color):
                 obj.refresh(children=True)