[Windows][Codex Desktop]Semi-transparent sidebar ignores the theme surface and falls back to system Mica

What version of the Codex App are you using (From “About Codex” dialog)?

26.814.41407

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Windows 11 x64, build 26200.7462

What issue are you seeing?

When using the ‘Everforest’ light theme, enabling Semi-transparent sidebar causes the sidebar and title bar to ignore the custom theme surface color and fall back to a cool system-white/Mica appearance.

My custom light theme uses:

• Surface/background: #FDF6E3
• Ink/foreground: #5C6A72
• Accent: #93B259
• Contrast: 45

With Semi-transparent sidebar disabled, the sidebar correctly uses a warm theme-derived surface (#F7F0DE).

With Semi-transparent sidebar enabled, the sidebar and title bar become approximately #F3F3F3 (cool system white), while the main content remains #FDF6E3. This creates a visibly inconsistent interface.

What steps can reproduce the bug?

1. On Windows, open Codex App.
2. Go to Settings → Appearance.
3. Select or configure a custom light theme with a warm surface color, for example #FDF6E3 (Everforest).
4. Keep the system and Codex theme in light mode.
5. Turn Semi-transparent sidebar off and observe that the sidebar follows the custom theme.
6. Turn Semi-transparent sidebar on.

What is the expected behavior?

Enabling Semi-transparent sidebar should preserve the custom theme’s visual direction—for example, by applying a translucent/tinted version of the configured surface color.

It should not silently replace the custom-themed sidebar and title bar with a system-white Mica surface while the rest of the application continues using the custom theme.

Additional information

_No response_