Guide · Agent skill
How to use the CSS @property Registration Guide agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The css-at-property skill is an agent skill that teaches an AI coding agent to register CSS custom properties with the @property rule. Registered properties can be animated by the browser and checked against a type, such as color or length. This guide explains what the skill does, how to install it, how to trigger it with natural requests, and what to watch for.
CSS @property Registration Guidethedaviddias/Front-End-Checklist · MIT Download the skill Quick start
- 1Download the ZIP. Download the skill ZIP from this page and unzip it. Confirm the folder contains SKILL.md and references/rule.md.
- 2Place the skill folder. Move the unzipped folder into ~/.claude/skills/ for personal use, or into a project's .claude/skills/ folder.
- 3Or upload it in the Claude apps. In the Claude apps, go to Settings → Capabilities → Skills and upload the skill.
- 4Make a natural request. Describe an animated gradient, a transition using custom properties, or a design token setup, and paste the relevant CSS.
- 5Review the registrations. Check each @property rule the agent adds for the correct syntax, an initial-value, and the inherits setting you want.
- 6Test in your target browsers. Run the changes in the browsers you support, since the skill does not cover fallbacks for older browsers.
What does the css-at-property skill make the agent do?
Custom properties (CSS variables) are untyped string substitutions by default, so the browser cannot interpolate them during a transition or animation. The skill makes the agent check whether custom properties used in transitions or animations are registered, and add @property rules where they are missing.
Each registration includes a syntax descriptor (for example color, length or number), an initial-value and an inherits setting. The agent then explains the result. The skill works through written CSS suggestions and reviews; it does not run code itself.
- Finds custom properties used in transitions or animations that have no @property registration
- Adds @property rules with syntax, initial-value and inherits
- Flags registrations that are missing an initial-value
- Explains how inherits controls cascade behaviour
How do you install the css-at-property skill?
Download the ZIP of the skill from this page and unzip it. The skill folder contains SKILL.md and references/rule.md. Put the unzipped folder in ~/.claude/skills/ to make it available to you across projects, or in a project's .claude/skills/ folder to share it with that project.
You can also upload the skill in the Claude apps by going to Settings → Capabilities → Skills.
- Personal install: ~/.claude/skills/
- Project install: the project's .claude/skills/ folder
- Claude apps: Settings → Capabilities → Skills, then upload the skill
How do you trigger the skill with natural requests?
You do not need to name the skill. The skill's description tells the agent when to use it, so ask for work that matches it: animated gradients, transitions that use CSS variables, or a typed design token system where invalid values should show errors.
Mention the specific problem. Include your CSS if you can, so the agent can review existing transitions rather than guess.
- "My gradient background doesn't animate when I change --brand-start. Can you fix the CSS?"
- "Review this stylesheet for custom properties used in transitions that aren't registered with @property."
- "Set up design tokens for colours and spacing so invalid values raise visible errors."
What does a registration look like?
A registration uses the @property rule with the custom property name and three descriptors. The syntax descriptor sets the type, initial-value sets the default, and inherits controls whether the value cascades to child elements. The example below comes from the skill's reference file.
The skill's guidance notes that inherits: false creates scoped tokens that do not cascade to children.
@property --property-name {
syntax: '<color>';
initial-value: #000;
inherits: true;
}What is the skill good for, and what does it not cover?
The skill suits front-end developers building animated gradients or transitions that use CSS variables, teams who want typed design tokens, and developers reviewing existing CSS for unregistered custom properties. It is not a fit for projects that must support older browsers: @property is not available everywhere, and the skill does not cover fallbacks in its file.
It is also unnecessary for simple styling work that neither animates nor types custom properties, and it has no relevance to JavaScript, backend or document tasks.
What does it need, and what are the safety notes?
The skill lists no requirements. It does not run scripts and does not use the network, so it only shapes the agent's written CSS suggestions and reviews. You still need to test the changes in the browsers you support.
The skill is released under the MIT licence.
- Requires: nothing listed
- Runs scripts: no
- Uses network: no
What people use it for
- Making a gradient background transition smoothly by registering its colour custom properties
- Finding unregistered custom properties used in existing animations during a CSS review
- Setting up typed design tokens for colours and lengths so misuse is caught
- Creating scoped component tokens with inherits: false
Frequently asked questions
How do I install the css-at-property agent skill?
Download the ZIP from this page and unzip it. Place the folder in ~/.claude/skills/ for personal use or in a project's .claude/skills/ folder. You can also upload it in the Claude apps under Settings → Capabilities → Skills.
What does the css-at-property skill require?
The skill lists no requirements. It does not run scripts and does not use the network. It works by guiding the agent's written CSS suggestions and reviews.
Is the css-at-property skill free to use?
The skill is released under the MIT licence. Check the licence file in the source repository for the full terms.
Does @property work in all browsers?
No. The skill notes that @property is not available everywhere, and it does not cover fallbacks for older browsers. Check which browsers you need to support before relying on it.
Why can't CSS custom properties be animated by default?
Custom properties are untyped string substitutions, so the browser does not know whether a value is a color, length or number. Registering the property with @property gives it a type so the browser can interpolate between values.
Can the skill run code or test my CSS?
No. The skill does not run code itself. It guides the agent's written suggestions and reviews, so you should test the output in a browser.
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Our verdict
Use this skill if you are building animated gradients or transitions driven by CSS variables, or setting up typed design tokens, and you target browsers that support @property. Pick something else if you need older browser support with fallbacks, or if your styling work does not involve animating or typing custom properties.
Download the skill