The one tell of AI-built sites, and a CSS block that fixes it

Developer Mert Url has identified a common aesthetic flaw in websites generated by AI coding agents: a lack of visual depth that makes pages appear like flat, colored-in mockups. To address this, he created 'unflat,' an open-source Agent Skill designed to automatically inject a CSS block that adds structure, lighting, and rhythm to web layouts. The tool analyzes a site's existing design tokens to implement subtle improvements, such as ground-level background adjustments, directional lighting, and mounted section surfaces. By avoiding the 'card-like' look, the CSS block creates a more professional, layered appearance without requiring manual markup changes. The skill is compatible with plain CSS and Tailwind, and it is intended to be used by AI agents like Claude Code or Cursor. The author invites developers to test the tool and provide feedback on how it handles various site architectures.