CSS Custom Property Bridge
Expose the design tokens as CSS variables so theming and styling can change at runtime.
What it adds
A generated layer of CSS custom properties mirroring the token source, which components are expected to style against.
What your agent is told to do
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What your agent is told to do
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Generate the custom properties from the same token source the rest of the app already uses, so a token and its variable can never disagree. A hand-maintained parallel list will drift within a release.
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Decide and document where each group of variables is declared — the document root for global theme values, a container for anything that must vary per section or per component — and apply that rule consistently.
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Fix the naming scheme and treat the generated names as a public contract, since stylesheets, components, and any customer-facing theming all reference them by name.
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Give every consumption point a fallback value so a component still renders sensibly when a variable is absent, which is the normal state during theme switching and partial loads.
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Coordinate with Unused Token Detection: that feature judges whether a token is still referenced, and it must be able to see references made through these variables, or every bridged token will look dead.
Edge cases it handles
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Edge cases it handles
7- A theme that defines only some of the variables must not leave components unstyled. Every reference needs a fallback, and the base theme must supply a complete set beneath any partial one.
- Scope decides behaviour: a variable declared at the document root affects everything, one declared on a container affects only its subtree. A value intended to vary per section but declared globally will leak into every other section on the page.
- Generated names must stay stable across builds. A name that changes because a build step reordered or hashed it will break every stylesheet and every customer theme that referenced it.
- Custom properties are readable by anything running on the page, so nothing derived from configuration, keys, entitlements, or internal identifiers may be emitted into them. Only presentation values belong here.
- Values that participate in animation or transition must be declared with a type, or the browser will step between them rather than interpolating.
- Switching themes must not repaint through an intermediate state where some variables have updated and others have not.
- A variable referencing another variable that is itself undefined resolves to nothing rather than to the fallback the author expected, so chains need a fallback at each step.
Definition of done
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Definition of done
9- Every custom property is generated from the token source, with no hand-maintained duplicates.
- The scope of each variable group is documented and matches where it is declared.
- Generated names are stable across builds and treated as a public contract.
- Every consumption point carries a fallback and renders sensibly under a partial theme.
- No configuration, credential, or internal identifier is exposed as a custom property.
- Theme switching applies in one pass with no visible intermediate state.
- Unused Token Detection resolves references made through the bridge.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
CSS Module Boundaries
CSS Module Boundaries
Keep each component's styles its own, and make the shared parts deliberate.
What it does
A boundary around each component's styles, exposing only a named set of hooks that callers are permitted to style through.
How it works
- 1 Identify the primitives the rest of the app builds on — button, field, card, menu, table — and treat everything inside them as private unless it is deliberately published.
- 2 For each primitive, publish an explicit surface: the variants it accepts, the slots a caller may target, and the custom properties it reads. Anything not on that list is internal and may change without notice.
- 3 Find the places where product screens currently reach into a primitive's internals and rewrite them to use the published surface, adding a variant or a slot where the need is legitimate.
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No account needed
Add this feature to my app:
https://addthisfeature.com/x/css-module-boundaries
Class Merge Helper
Class Merge Helper
Combine conditional classes in one place so the last one written actually wins.
What it does
A single helper every component uses to resolve base, conditional, and caller-supplied classes into one final list.
How it works
- 1 Find every component that currently builds a class string by hand and route all of them through one helper, so the resolution rules are identical everywhere.
- 2 Define the precedence plainly: the component's own base classes lose to its variant classes, and both lose to whatever the caller passed in. A caller that supplies a class expects it to take effect.
- 3 Accept the shapes calling code actually produces rather than forcing every call site to normalise first, and make the behaviour for absent and empty values explicit rather than incidental.
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No account needed
Add this feature to my app:
https://addthisfeature.com/x/class-merge-helper
CSS Layer Strategy
CSS Layer Strategy
Give the stylesheet an explicit order of precedence instead of one decided by accident.
What it does
An ordered set of cascade layers — reset, tokens, base, components, utilities, overrides — that every stylesheet is assigned to.
How it works
- 1 Define the layer order once, in one file, and have every other stylesheet declare which layer it belongs to rather than relying on the order the bundler happens to emit.
- 2 Assign the existing stylesheets to layers before changing any of them. The map from current file to intended layer is the whole design decision, and it should be reviewable on its own.
- 3 Migrate in stages: place everything currently unlayered into a defined position relative to the new layers, then move files into their proper layer one at a time, checking the rendered result after each move.
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No account needed
Add this feature to my app:
https://addthisfeature.com/x/css-layer-strategy
How it works
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Copy the link
Grab the Markdown instruction URL for this feature.
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Give it to your AI
Paste it into Claude Code, Cursor, v0, Lovable — whatever you build with.
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It inspects, then implements
Your agent reads your existing app first, then adds the feature to fit it.
Works with your stack
These instructions are written to adapt. They tell the agent to detect your framework, match your existing design system, and reuse what you already have — rather than assuming a particular stack.
Need it tighter than that? Customize the feature and tell it exactly what you're running.