Feature request: Improve Codex CLI output readability with syntax highlighting and visual hierarchy

What feature would you like to see?

Summary

Codex CLI frequently outputs large amounts of generated code and explanations during normal usage.
Currently, most of this output is rendered as plain white text, which makes long sessions hard to read, review, and reason about.

This feature request focuses specifically on output readability and visual structure, not overall theming or cosmetic customization.

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Problems observed

• Generated code lacks syntax highlighting
• Explanations, code blocks, file paths, and warnings share the same visual style
• Important structural boundaries (e.g. where generated code begins or ends) are not visually distinct
• The UI feels visually flat and cognitively tiring during long or iterative sessions

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Proposed improvements (scoped)

The goal is to introduce lightweight visual hierarchy, not heavy theming:

• Syntax highlighting for generated code blocks
• Clear visual separation between:

• Explanations / reasoning
• Code blocks
• File paths / filenames
• Warnings or destructive actions
• Subtle use of color to establish hierarchy (headers, boxes, separators), rather than decoration
• Improve readability without requiring additional configuration from the user

Even modest changes here would significantly reduce cognitive load and make Codex CLI feel more production-grade for long-running workflows.

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Why this matters

Codex CLI is positioned as a serious, agentic developer tool.
Visual clarity directly affects:

• Speed and accuracy of code review
• User confidence in generated output
• Comfort during long sessions

At the moment, the functionality is strong, but the UI undersells it.

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Optional note (visual affordances)

As a small but high-impact improvement avoided by the current white-on-black output, structural UI elements such as headers or welcome boxes could benefit from a subtle accent color to signal hierarchy.

For example, using a calm, readable accent color (e.g. #7ec8e3) for non-code structural elements could help guide the eye without introducing heavy theming or visual noise.

This is less about aesthetics and more about providing clear visual affordances in a dense, text-heavy interface.

Additional information

_No response_