Windows Codex app header and left sidebar become transparent when maximized

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

OpenAI.Codex Microsoft Store package 26.527.3686.0; PackageFullName OpenAI.Codex_26.527.3686.0_x64__2p2nqsd0c76g0; Codex.exe product/file version 148.0.7778.179

What subscription do you have?

Unknown

What platform is your computer?

Microsoft Windows NT 10.0.19045.0 x64

What issue are you seeing?

When the Codex desktop app is maximized on Windows, the app chrome/header area and left sidebar/window edge area appear partially transparent. The Windows desktop wallpaper and desktop icons can be seen through the Codex window at the top and left edges.

The main app content area remains mostly white/opaque, but the header/sidebar surfaces appear translucent. This is visually significant because desktop content behind the app remains visible through what should be opaque Codex UI surfaces.

A screenshot is available, but it contains visible desktop file names/icons, so I am not attaching it publicly unless requested.

What steps can reproduce the bug?

1. Launch the Codex desktop app from the Microsoft Store package on Windows.
2. Open a thread.
3. Maximize the Codex window.
4. Observe the top header/title area and left sidebar/window edge area.

Actual result: the header and left side of the maximized Codex window are partially transparent, showing the Windows desktop behind the app.

This appears to reproduce with Windows transparency effects enabled.

What is the expected behavior?

The Codex app header and sidebar/window background should be fully opaque when the app is maximized, matching the rest of the app surface and preventing desktop content from showing through.

Additional information

Additional environment:

• OS: Microsoft Windows 10 Pro, build 19045, 64-bit
• Display: 3840 x 2160, 32-bit color
• GPU: NVIDIA GeForce RTX 4060 Ti
• GPU driver: 32.0.16.1047, driver date 2026-05-19
• Windows transparency setting: enabled (HKCU\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize EnableTransparency = 1)
• App source: Microsoft Store
• winget upgrade --id 9PLM9XGG6VKS --source msstore reports no available upgrade

winget output:
No available upgrade found.
No newer package versions are available from the configured sources.

Package details:
Name: OpenAI.Codex
Version: 26.527.3686.0
SignatureKind: Store
InstallLocation: C:\Program Files\WindowsApps\OpenAI.Codex_26.527.3686.0_x64__2p2nqsd0c76g0