CSS Module Boundaries
Keep each component's styles its own, and make the shared parts deliberate.
What it adds
A boundary around each component's styles, exposing only a named set of hooks that callers are permitted to style through.
What your agent is told to do
5
What your agent is told to do
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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.
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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.
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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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Make the boundary enforceable rather than advisory, so a reach-in selector is caught during review or in the build instead of being discovered when a primitive is refactored months later.
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Do not attempt to solve precedence here. Which rule wins when two collide belongs to CSS Layer Strategy; this feature decides who is allowed to write the second rule at all.
Edge cases it handles
7
Edge cases it handles
7- Selectors that reach past a component's root into its internal elements must be rejected, because they silently couple a screen to markup the primitive's author is free to change.
- Theming needs a defined way in. Publish the named custom properties a component reads and let callers set those, rather than leaving people to guess and target internal class names.
- Composition between modules must not become circular. A chain in which one component's styles compose from another that composes back produces an order that depends on import sequence and will differ between builds.
- Product screens overriding a primitive's internals is the exact failure this feature exists to stop, and it must be treated as a defect rather than a shortcut, even when the override is small and works today.
- Generated or utility class names that appear inside a primitive are still internal; a caller matching on them has reached in by another route.
- Some overrides are genuinely necessary before the right variant exists. Give them a marked, temporary escape hatch that is visible in a search, rather than pretending the need does not arise.
- A component rendering into a portal or an overlay leaves its parent's scope, so styles that relied on ancestry will stop applying and must be passed in deliberately.
Definition of done
8
Definition of done
8- Every shared primitive has a documented public surface of variants, slots, and custom properties.
- No product screen selector targets a primitive's internal elements.
- Theming happens through published custom properties rather than internal class names.
- Module composition has no cycles and produces the same result regardless of import order.
- Boundary violations are caught by review or by the build, not at runtime.
- Temporary overrides are marked and findable by search.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Variant Class Generator
Variant Class Generator
Declare a component's variants once instead of scattering conditionals through its markup.
What it does
A declarative variant definition per component mapping size, tone, and state to the classes each combination produces.
How it works
- 1 Find the components whose markup is threaded with conditional class logic and replace that logic with a single declaration listing each variant, its options, and its default.
- 2 Support combinations that are more than the sum of their parts, so a specific pairing of size and tone can produce classes that neither produces alone, without reintroducing a conditional in the markup.
- 3 Make invalid combinations impossible to express rather than merely undesirable, and give the component a defined appearance when it receives a combination it does not recognise.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/variant-class-generator
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.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/class-merge-helper
Tokenized Inline Styles
Tokenized Inline Styles
Allow styles computed at runtime without letting arbitrary values escape the design system.
What it does
A constrained path for dynamically computed styles, where every value is either a design token or a number clamped to an approved range.
How it works
- 1 Find every place the app already sets a style value at runtime — progress widths, chart bar heights, avatar colours, drag positions, user-chosen accent colours — and sort them into two groups: values that must come from the token set, and values that are genuinely continuous numbers.
- 2 For the first group, accept only token names and resolve them to values at the boundary. A caller passing a raw colour or a raw pixel value should be rejected loudly in development rather than quietly rendered.
- 3 For the second group, clamp to a documented minimum and maximum and round to a sensible precision, so a percentage of 4000 or a width of 0.3847291 pixels never reaches the DOM.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/tokenized-inline-styles
How it works
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1
Copy the link
Grab the Markdown instruction URL for this feature.
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2
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.