Windows 10 desktop app: sidebar background becomes transparent when maximized and focused

Summary

On Windows 10, the Codex desktop app sidebar/titlebar background becomes transparent when the window is maximized and focused. The desktop wallpaper shows through the sidebar area, while the sidebar text and controls still render.

When the same maximized Codex window loses focus, the sidebar background renders normally again. When the window is not maximized, it also renders normally.

Environment

• OS: Windows 10
• App: Codex Desktop for Windows
• Codex version: 26.527.31326

Steps to reproduce

1. Open Codex Desktop on Windows 10.
2. Maximize the Codex window.
3. Focus the Codex window.
4. Observe the left sidebar/titlebar background becomes transparent and the desktop wallpaper shows behind it.
5. Focus another window while Codex remains maximized.
6. Observe the sidebar/titlebar background returns to normal.

Expected behavior

The sidebar/titlebar background should remain opaque in all focus and maximized states.

Actual behavior

The sidebar/titlebar background becomes transparent only when Codex is maximized and focused. Sidebar text and controls remain visible.

Notes

I have screenshots showing both states:

• CoxexWithBugCapture.JPG: maximized + focused, bug visible
• CodexWithNoBugWhenNotInFofus.JPG: maximized + unfocused, no bug
• version.JPG: About dialog showing Codex version 26.527.31326

The issue appears specific to the combination Windows 10 + maximized window + focused Codex window, possibly related to the desktop shell/window compositing layer or active-window transparency/acrylic handling.