How to use the CSS Layout Expert agent skill (css-expert)

What is the css-expert skill and what does it make the agent do?

An agent skill is a folder containing instructions that an AI agent reads when a task matches the skill. The css-expert skill covers flexbox, grid, animations, responsive design and modern layout techniques. Its single file, SKILL.md, sets out principles the agent should follow when it writes CSS.

The skill is guidance, not a tool. It does not run code, open a browser or inspect your page. It changes how the agent writes CSS: for example, it steers the agent toward flexbox for single-direction layouts and grid for two-directional ones, toward container queries and clamp() for responsive sizing, and away from fixed pixel widths, arbitrary z-index values and needless !important overrides.

• Uses flexbox for rows or columns and CSS Grid for layouts with rows and columns together
• Uses custom properties for theming, spacing scales and dark mode
• Designs mobile-first with min-width media queries
• Prefers logical properties such as inline-start over left
• Uses @layer to manage specificity instead of !important
• Recommends transform and opacity for smooth animation and 150-300ms transitions on interactive states

Install the css-expert skill from the ZIP download

Download the css-expert ZIP from this page and unzip it. The folder contains SKILL.md. Then place the folder where your agent looks for skills. You have two options: a personal install for all your projects, or a project install that only applies to one codebase.

For a personal install, put the skill in ~/.claude/skills/. For a project install, put it in the .claude/skills/ folder inside your project. If you use the Claude apps instead, you can upload the ZIP under Settings → Capabilities → Skills.

• Personal: ~/.claude/skills/css-expert/
• Project: .claude/skills/css-expert/ inside your project folder
• Claude apps: Settings → Capabilities → Skills, then upload the ZIP

Trigger the skill with natural requests

You do not need a special command. The agent uses the skill when your request matches its description, which covers CSS, layout, flexbox, grid, animations and responsive design. Ask in plain language about the page or component you want to build.

Be specific about the layout you need and the constraints that matter, such as the browsers you must support or whether the page must support dark mode. The guidance assumes current CSS features, so say so if your project is older.

• Make a responsive three-column card grid that becomes one column on small screens
• Add a dark mode to this page using CSS custom properties
• Center this modal vertically and horizontally using flexbox
• Make the heading size scale smoothly between mobile and desktop without breakpoints

Examples of what the agent will produce

Because the skill favours modern techniques, the agent will often reach for specific patterns. Expect fluid type with clamp(1rem, 2.5vw, 2rem), auto-fit grids with minmax() instead of media queries, aspect-ratio instead of the padding-bottom hack, and colour tokens defined on :root and swapped for dark mode.

Review the output as you would any code. The skill tells the agent what good practice looks like, but it cannot confirm that the result renders correctly in your target browsers.

Safety notes: scripts and network access

According to the skill's listing, css-expert requires nothing beyond the agent itself, does not run scripts and does not use the network. Its only file is SKILL.md, so there is no executable code to review beyond the written guidance.

Because it is only text instructions, it will not change files or fetch resources on its own. Any file edits come from the agent working on your request, so keep your normal review habits.

• Runs scripts: no
• Uses network: no
• Requires: nothing listed
• Files: SKILL.md

Tips for better CSS from the agent

Give the agent your existing tokens or spacing scale so it reuses them rather than inventing new ones. Ask it to explain its layout choice if you want to learn the reasoning, since the skill is built around clear principles like one-dimensional versus two-dimensional layout.

If you are working in a legacy codebase, state the browser support requirements at the start. The skill's guidance assumes current features, so the agent may otherwise use container queries or :has() where your users cannot.

• Paste your existing custom properties so the agent extends them
• Ask for a z-index scale in custom properties if your page has layered components
• Check browser support for any vendor-prefix or newer feature before shipping