Start with a wide image
A 16:10 or wider source gives the builder room to crop across laptop and desktop windows. Use at least 1600 pixels on the long edge, but avoid enormous files that add no visible detail.
Codex custom background
A Codex background should frame the work—not fight it.
Use image position, dimming, blur and panel opacity together. CodexSkin previews the actual reading surfaces and exports a reversible, data-only theme package.
Good subject placement
Keep detail away from the reading column.
The open left side gives navigation and task text a calm foundation while the focal image remains visible.
Choose a quiet text zone
Position faces, characters and high-contrast detail away from the main reading column. A useful image often has deliberate negative space rather than a centered subject.
Dim before you blur
Dimming preserves the image structure while lowering visual competition. Add modest blur only when fine detail still interferes with text. Too much blur creates a muddy color field.
Why not patch app.asar?
Prefer a reversible boundary.
Patching an application package couples a visual preference to official files, signatures and update behavior. The current Dream Skin engine instead starts a local themed session and uses loopback CDP. That approach still has a meaningful local-security tradeoff, but it leaves the official install directory untouched and provides a stock restore path.
The background itself belongs in a constrained package. Theme authors should be able to choose an image, crop and allowlisted visual values—never executable logic. If a downloaded “theme” asks you to run its own shell or PowerShell command, treat it as software and review it as software.