[macOS][Codex App] Selected text has insufficient contrast in Dark appearance

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

26.814.41407 (Build 6720)

What subscription do you have?

Plus

What platform is your computer?

Darwin 25.6.0 arm64 arm

What issue are you seeing?

On macOS when the system is using Dark appearance, dragging across text in the Codex App produces a selection that is technically present but has very low visual contrast. The selected range can look almost identical to the surrounding unselected text/background, making it appear as if nothing was selected.

This is a visual/accessibility problem rather than a failure to select text: the selection can still be copied or acted on, but the highlight is not sufficiently visible. The same interaction is noticeably clearer when the system is using Light appearance.

What steps can reproduce the bug?

1. Set macOS System Settings → Appearance to Dark.
2. Open the Codex App and open a task containing a multi-line response.
3. Click/press and drag across part of the response text with a mouse or trackpad.
4. Observe the selected range while the pointer is still held and after releasing it.
5. Compare the selected range with the surrounding text, or repeat the same steps in Light appearance.

What is the expected behavior?

Selected text should have a clearly distinguishable, theme-appropriate highlight in Dark appearance. Both the selection background and foreground text should maintain sufficient contrast against the surrounding surface and remain visually obvious during and after a drag selection.

Additional information

The symptom points to the packaged frontend's text-selection/theme styling (for example, a ::selection rule or selection color token) not providing enough contrast in the dark theme. A robust fix would use a dedicated dark-theme selection token, or the native/system accent selection colors, with contrast checks for both normal and high-contrast display settings. The selection styling should be applied consistently to assistant text, user text, code/Markdown content, and any portaled text surfaces.

A local experiment against the installed packaged app confirmed that increasing the dark-theme selection contrast resolves the visual symptom. This was only a local validation of the behavior; the desktop app's original frontend source is not part of this public repository, so no compiled app bundle or local files are attached.

I searched existing open issues for macOS text-selection and selected-text reports. Issues such as #36288 and #25641 concern the selected-text action toolbar (clipping or missing actions), and #38862 concerns severe slowdown during selection; they do not cover this dark-mode selection-contrast problem.

No source file or test entry point is identified; the issue says the desktop app's original frontend source is not in this public repository. First reproduce the selection in macOS Dark appearance using the listed steps and compare it with Light appearance. Done means selected text has a clearly distinguishable, theme-appropriate highlight across the mentioned text surfaces.