Review CSS custom properties, often called CSS variables, used in animations and transitions. Add @property registrations with value types, initial values, and inheritance settings to support smooth changes and validate assigned values.
Use when implementing animated gradients, complex CSS transitions that involve custom property values, or building a typed design token system where custom property misuse should produce visible errors.
Review the instructions the agent will receive before you install.
CSS custom properties are powerful but limited by default: they are untyped string substitutions that the browser cannot interpolate during transitions or animations. Registering a property with @property gives the browser the information it needs to animate between values, validate token assignments, and scope inheritance — turning custom properties from string macros into first-class typed values. This unlocks gradient animations, typed design tokens, and scoped component theming that are impossible with unregistered properties.
Review the CSS custom properties in this file. Identify any properties that are used in transitions or animations — these require @property registration to animate correctly.
Add @property registrations for the custom properties used in transitions or animations in this CSS. Include the correct syntax descriptor, an initial-value, and the appropriate inherits value.
Explain how @property works, why unregistered custom properties cannot be animated, what the syntax descriptor values mean, and how inherits controls cascade behaviour.
Inspect all CSS transitions and animations that reference custom properties. Flag any custom property used in a transition or animation that is not registered with @property, and flag any @property registration that is missing initial-value.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/css/css-at-property
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