diff --git a/CHANGELOG.md b/CHANGELOG.md
index 114d3b7..7fd84be 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,12 @@ and this project adheres to Semantic Calendar Versioning with format YYYY.MM.DD.
 
 ## [Unreleased]
 
+### Fixed
+- **TUI Compatibility**: Fixed stylesheet error with Textual 6.x
+  - Added missing `$panel` CSS variable to both classic and turbo TUI themes
+  - Resolves "reference to undefined variable '$panel'" error when starting TUI with `-t classic` or `-t turbo` options
+  - Maps `panel` to `surface` color for consistent UI appearance
+
 ### Changed
 - **Bot Messages**: Updated task start confirmation to use proper British Army Voice Procedure
   - Changed "Roger that!" to "Roger!" (single word affirmative as per military radio protocol)
diff --git a/chatrixcd/tui.py b/chatrixcd/tui.py
index b252bcd..6b106b6 100644
--- a/chatrixcd/tui.py
+++ b/chatrixcd/tui.py
@@ -1706,6 +1706,7 @@ def get_css_variables(self) -> Dict[str, str]:
             'text': theme['text'],
             'text-muted': theme['text-muted'],
             'foreground': theme['text'],  # Alias for Textual 6.x compatibility
+            'panel': theme['surface'],  # Panel color for Textual 6.x compatibility
         }
         
     def compose(self) -> ComposeResult:
diff --git a/chatrixcd/tui_turbo.py b/chatrixcd/tui_turbo.py
index f7ab377..be3641b 100644
--- a/chatrixcd/tui_turbo.py
+++ b/chatrixcd/tui_turbo.py
@@ -606,6 +606,7 @@ def get_css_variables(self) -> Dict[str, str]:
             'text': theme['text'],
             'text-muted': theme['text-muted'],
             'foreground': theme['text'],  # Alias for Textual 6.x compatibility
+            'panel': theme['surface'],  # Panel color for Textual 6.x compatibility
         }
     
     def compose(self) -> ComposeResult: