React.js • Chapter 43 • Foundations to Advanced
CSS Modules and Design Systems
Study each React concept through explanations, focused examples, code, reasoning, expected behavior, practice, and review.
43.1 CSS Module Basics
CSS Module Basics is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs. In Chapter 43, the purpose is to make the behavior observable rather than memorizing an API. Follow the value from its source through the component tree and identify what React needs in order to produce the next interface. This section 43.1 connects the idea directly to CSS Modules and Design Systems.
For CSS Module Basics, inspect inputs, component ownership, visible output, edge cases, and the reason another render occurs. A reliable React design makes ownership explicit, keeps rendering predictable, and separates calculations from synchronization with external systems. When a feature seems complicated, reduce it to one component, one state change, or one boundary and rebuild from that verified behavior. In CSS Modules and Design Systems, keep the CSS Module Basics responsibility visible while you test it.
This topic emphasizes structure. Use complete states for loading, success, empty data, and failure when those states can occur. After the example works, explain why React rendered what you see and which change would cause another render; that reasoning is more valuable than copying syntax. For section 43.1, relate that explanation back to CSS Module Basics.
Key terms in plain language
- Interface contract — the behavior users and other components can rely on.
- Module — a focused part of css module basics used to describe one responsibility, input, rendering decision, or boundary in the interface.
- Basics — a focused part of css module basics used to describe one responsibility, input, rendering decision, or boundary in the interface.
10 teaching examples
Example 1: Accessibility check
Use CSS Module Basics in the Task board while testing keyboard access, semantic markup, labels, focus order, and understandable status feedback. React does not replace browser accessibility rules, so verify the generated interface.
Example 2: State ownership check
For the Notification center, identify which component truly owns the information involved in CSS Module Basics. Remove duplicated state and derive values during rendering when they can be calculated from existing props or state. CSS Module Basics is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 3: Network-delay scenario
Assume the Quiz screen is waiting on a slow API while using CSS Module Basics. Decide what stays interactive, what shows pending feedback, what can be cancelled, and how stale responses are prevented from replacing newer data.
Example 4: Refactoring exercise
Take a large Language selector component that mixes CSS Module Basics with unrelated concerns. Extract one focused component or custom hook, give it a narrow API, and confirm that the user-visible behavior stays the same.
Example 5: Performance experiment
Profile the Account menu before optimizing CSS Module Basics. Record which components render, what calculation is costly, and whether the delay is actually noticeable; apply an optimization only when the measurement supports it. CSS Module Basics is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 6: Production review
Assume the Data table feature using CSS Module Basics ships to many devices and languages. Review error recovery, loading states, accessibility, RTL layout, small-screen width, security boundaries, and whether monitoring can reveal failures.
Example 7: Smallest useful case
Create the smallest working version of CSS Module Basics inside a Dashboard filter. Keep one input and one visible result, then describe inputs, component ownership, visible output, edge cases, and the reason another render occurs. This gives you a baseline before extra features hide the important behavior. CSS Module Basics is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 8: Change one input
Keep the Message composer example stable but change one input that affects CSS Module Basics. Predict what React will render before running the code, then compare the result with your prediction and explain the render path.
Example 9: Two-component comparison
Build one version of the Appointment form with the CSS Module Basics responsibility in the parent and another with it in the child. Compare data ownership, reuse, and how many components need to know about the decision. CSS Module Basics is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 10: Failure or edge case
Create a safe edge case for CSS Module Basics in the Photo gallery: empty data, a missing prop, a rejected request, rapid clicks, or an unmounted element. Show the user a clear state instead of allowing confusing or stale output.
React coding example
export default function TopicDemo() {
return (
<section aria-labelledby="topic-title" className="topic-panel">
<h2 id="topic-title">{"CSS Module Basics"}</h2>
<label>
Search
<input name="search" autoComplete="off" />
</label>
<button type="button">Apply</button>
</section>
);
}Step-by-step code explanation
- Identify the responsibility demonstrated by CSS Module Basics.
- Read the component from inputs to returned JSX before focusing on individual syntax.
- Trace which event, prop, promise, or state update can cause the visible result to change.
- Test one normal path and one edge case so the behavior is not inferred from the happy path alone.
- Keep the example small enough that you can explain every render and every external side effect.
Expected behavior: A small React interface demonstrating CSS Module Basics; the exact browser text depends on the interaction or data used in the example.
Practice exercise
Create a small interface focused on CSS Module Basics. Write the expected screen state before running it, test one edge case, and change one input or interaction. Then explain which component owns the relevant data, what caused the render, and one accessibility or small-screen check you would perform before shipping the feature. Record the result as the Chapter 43 practice for CSS Modules and Design Systems.
43.2 Scoped Class Names
Scoped Class Names is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs. In Chapter 43, the purpose is to make the behavior observable rather than memorizing an API. Follow the value from its source through the component tree and identify what React needs in order to produce the next interface. This section 43.2 connects the idea directly to CSS Modules and Design Systems.
For Scoped Class Names, inspect inputs, component ownership, visible output, edge cases, and the reason another render occurs. A reliable React design makes ownership explicit, keeps rendering predictable, and separates calculations from synchronization with external systems. When a feature seems complicated, reduce it to one component, one state change, or one boundary and rebuild from that verified behavior. In CSS Modules and Design Systems, keep the Scoped Class Names responsibility visible while you test it.
This topic emphasizes data flow. Use complete states for loading, success, empty data, and failure when those states can occur. After the example works, explain why React rendered what you see and which change would cause another render; that reasoning is more valuable than copying syntax. For section 43.2, relate that explanation back to Scoped Class Names.
Key terms in plain language
- Interface contract — the behavior users and other components can rely on.
- Scoped — a focused part of scoped class names used to describe one responsibility, input, rendering decision, or boundary in the interface.
- Class — a focused part of scoped class names used to describe one responsibility, input, rendering decision, or boundary in the interface.
- Names — a focused part of scoped class names used to describe one responsibility, input, rendering decision, or boundary in the interface.
10 teaching examples
Example 1: State ownership check
For the Account menu, identify which component truly owns the information involved in Scoped Class Names. Remove duplicated state and derive values during rendering when they can be calculated from existing props or state. Scoped Class Names is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 2: Network-delay scenario
Assume the Data table is waiting on a slow API while using Scoped Class Names. Decide what stays interactive, what shows pending feedback, what can be cancelled, and how stale responses are prevented from replacing newer data.
Example 3: Refactoring exercise
Take a large Upload panel component that mixes Scoped Class Names with unrelated concerns. Extract one focused component or custom hook, give it a narrow API, and confirm that the user-visible behavior stays the same.
Example 4: Performance experiment
Profile the Team roster before optimizing Scoped Class Names. Record which components render, what calculation is costly, and whether the delay is actually noticeable; apply an optimization only when the measurement supports it. Scoped Class Names is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 5: Production review
Assume the Analytics card feature using Scoped Class Names ships to many devices and languages. Review error recovery, loading states, accessibility, RTL layout, small-screen width, security boundaries, and whether monitoring can reveal failures.
Example 6: Smallest useful case
Create the smallest working version of Scoped Class Names inside a Photo gallery. Keep one input and one visible result, then describe inputs, component ownership, visible output, edge cases, and the reason another render occurs. This gives you a baseline before extra features hide the important behavior. Scoped Class Names is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 7: Change one input
Keep the Task board example stable but change one input that affects Scoped Class Names. Predict what React will render before running the code, then compare the result with your prediction and explain the render path.
Example 8: Two-component comparison
Build one version of the Notification center with the Scoped Class Names responsibility in the parent and another with it in the child. Compare data ownership, reuse, and how many components need to know about the decision. Scoped Class Names is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 9: Failure or edge case
Create a safe edge case for Scoped Class Names in the Quiz screen: empty data, a missing prop, a rejected request, rapid clicks, or an unmounted element. Show the user a clear state instead of allowing confusing or stale output.
Example 10: Accessibility check
Use Scoped Class Names in the Language selector while testing keyboard access, semantic markup, labels, focus order, and understandable status feedback. React does not replace browser accessibility rules, so verify the generated interface.
React coding example
export default function TopicDemo() {
return (
<section aria-labelledby="topic-title" className="topic-panel">
<h2 id="topic-title">{"Scoped Class Names"}</h2>
<label>
Search
<input name="search" autoComplete="off" />
</label>
<button type="button">Apply</button>
</section>
);
}Step-by-step code explanation
- Identify the responsibility demonstrated by Scoped Class Names.
- Read the component from inputs to returned JSX before focusing on individual syntax.
- Trace which event, prop, promise, or state update can cause the visible result to change.
- Test one normal path and one edge case so the behavior is not inferred from the happy path alone.
- Keep the example small enough that you can explain every render and every external side effect.
Expected behavior: A small React interface demonstrating Scoped Class Names; the exact browser text depends on the interaction or data used in the example.
Practice exercise
Create a small interface focused on Scoped Class Names. Write the expected screen state before running it, test one edge case, and change one input or interaction. Then explain which component owns the relevant data, what caused the render, and one accessibility or small-screen check you would perform before shipping the feature. Record the result as the Chapter 43 practice for CSS Modules and Design Systems.
43.3 Design Tokens
Design Tokens is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs. In Chapter 43, the purpose is to make the behavior observable rather than memorizing an API. Follow the value from its source through the component tree and identify what React needs in order to produce the next interface. This section 43.3 connects the idea directly to CSS Modules and Design Systems.
For Design Tokens, inspect trust boundaries, server verification, token exposure, unsafe HTML, and authorization decisions. A reliable React design makes ownership explicit, keeps rendering predictable, and separates calculations from synchronization with external systems. When a feature seems complicated, reduce it to one component, one state change, or one boundary and rebuild from that verified behavior. In CSS Modules and Design Systems, keep the Design Tokens responsibility visible while you test it.
This topic emphasizes edge cases. Use complete states for loading, success, empty data, and failure when those states can occur. After the example works, explain why React rendered what you see and which change would cause another render; that reasoning is more valuable than copying syntax. For section 43.3, relate that explanation back to Design Tokens.
Key terms in plain language
- Interface contract — the behavior users and other components can rely on.
- Design — a focused part of design tokens used to describe one responsibility, input, rendering decision, or boundary in the interface.
- Tokens — a focused part of design tokens used to describe one responsibility, input, rendering decision, or boundary in the interface.
10 teaching examples
Example 1: Network-delay scenario
Assume the Analytics card is waiting on a slow API while using Design Tokens. Decide what stays interactive, what shows pending feedback, what can be cancelled, and how stale responses are prevented from replacing newer data.
Example 2: Refactoring exercise
Take a large Booking flow component that mixes Design Tokens with unrelated concerns. Extract one focused component or custom hook, give it a narrow API, and confirm that the user-visible behavior stays the same.
Example 3: Performance experiment
Profile the Support ticket before optimizing Design Tokens. Record which components render, what calculation is costly, and whether the delay is actually noticeable; apply an optimization only when the measurement supports it. Design Tokens is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 4: Production review
Assume the Lesson tracker feature using Design Tokens ships to many devices and languages. Review error recovery, loading states, accessibility, RTL layout, small-screen width, security boundaries, and whether monitoring can reveal failures.
Example 5: Smallest useful case
Create the smallest working version of Design Tokens inside a Quiz screen. Keep one input and one visible result, then describe trust boundaries, server verification, token exposure, unsafe HTML, and authorization decisions. This gives you a baseline before extra features hide the important behavior. Design Tokens is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 6: Change one input
Keep the Language selector example stable but change one input that affects Design Tokens. Predict what React will render before running the code, then compare the result with your prediction and explain the render path.
Example 7: Two-component comparison
Build one version of the Account menu with the Design Tokens responsibility in the parent and another with it in the child. Compare data ownership, reuse, and how many components need to know about the decision. Design Tokens is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 8: Failure or edge case
Create a safe edge case for Design Tokens in the Data table: empty data, a missing prop, a rejected request, rapid clicks, or an unmounted element. Show the user a clear state instead of allowing confusing or stale output.
Example 9: Accessibility check
Use Design Tokens in the Upload panel while testing keyboard access, semantic markup, labels, focus order, and understandable status feedback. React does not replace browser accessibility rules, so verify the generated interface.
Example 10: State ownership check
For the Team roster, identify which component truly owns the information involved in Design Tokens. Remove duplicated state and derive values during rendering when they can be calculated from existing props or state. Design Tokens is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
React coding example
export default function TopicDemo() {
return (
<section aria-labelledby="topic-title" className="topic-panel">
<h2 id="topic-title">{"Design Tokens"}</h2>
<label>
Search
<input name="search" autoComplete="off" />
</label>
<button type="button">Apply</button>
</section>
);
}Step-by-step code explanation
- Identify the responsibility demonstrated by Design Tokens.
- Read the component from inputs to returned JSX before focusing on individual syntax.
- Trace which event, prop, promise, or state update can cause the visible result to change.
- Test one normal path and one edge case so the behavior is not inferred from the happy path alone.
- Keep the example small enough that you can explain every render and every external side effect.
Expected behavior: A small React interface demonstrating Design Tokens; the exact browser text depends on the interaction or data used in the example.
Practice exercise
Create a small interface focused on Design Tokens. Write the expected screen state before running it, test one edge case, and change one input or interaction. Then explain which component owns the relevant data, what caused the render, and one accessibility or small-screen check you would perform before shipping the feature. Record the result as the Chapter 43 practice for CSS Modules and Design Systems.
43.4 Reusable UI Primitives
Reusable UI Primitives is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs. In Chapter 43, the purpose is to make the behavior observable rather than memorizing an API. Follow the value from its source through the component tree and identify what React needs in order to produce the next interface. This section 43.4 connects the idea directly to CSS Modules and Design Systems.
For Reusable UI Primitives, inspect inputs, component ownership, visible output, edge cases, and the reason another render occurs. A reliable React design makes ownership explicit, keeps rendering predictable, and separates calculations from synchronization with external systems. When a feature seems complicated, reduce it to one component, one state change, or one boundary and rebuild from that verified behavior. In CSS Modules and Design Systems, keep the Reusable UI Primitives responsibility visible while you test it.
This topic emphasizes accessibility. Use complete states for loading, success, empty data, and failure when those states can occur. After the example works, explain why React rendered what you see and which change would cause another render; that reasoning is more valuable than copying syntax. For section 43.4, relate that explanation back to Reusable UI Primitives.
Key terms in plain language
- Interface contract — the behavior users and other components can rely on.
- Reusable — a focused part of reusable ui primitives used to describe one responsibility, input, rendering decision, or boundary in the interface.
- Primitives — a focused part of reusable ui primitives used to describe one responsibility, input, rendering decision, or boundary in the interface.
10 teaching examples
Example 1: Refactoring exercise
Take a large Course catalog component that mixes Reusable UI Primitives with unrelated concerns. Extract one focused component or custom hook, give it a narrow API, and confirm that the user-visible behavior stays the same.
Example 2: Performance experiment
Profile the Profile settings before optimizing Reusable UI Primitives. Record which components render, what calculation is costly, and whether the delay is actually noticeable; apply an optimization only when the measurement supports it. Reusable UI Primitives is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 3: Production review
Assume the Search panel feature using Reusable UI Primitives ships to many devices and languages. Review error recovery, loading states, accessibility, RTL layout, small-screen width, security boundaries, and whether monitoring can reveal failures.
Example 4: Smallest useful case
Create the smallest working version of Reusable UI Primitives inside a Data table. Keep one input and one visible result, then describe inputs, component ownership, visible output, edge cases, and the reason another render occurs. This gives you a baseline before extra features hide the important behavior. Reusable UI Primitives is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 5: Change one input
Keep the Upload panel example stable but change one input that affects Reusable UI Primitives. Predict what React will render before running the code, then compare the result with your prediction and explain the render path.
Example 6: Two-component comparison
Build one version of the Team roster with the Reusable UI Primitives responsibility in the parent and another with it in the child. Compare data ownership, reuse, and how many components need to know about the decision. Reusable UI Primitives is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 7: Failure or edge case
Create a safe edge case for Reusable UI Primitives in the Analytics card: empty data, a missing prop, a rejected request, rapid clicks, or an unmounted element. Show the user a clear state instead of allowing confusing or stale output.
Example 8: Accessibility check
Use Reusable UI Primitives in the Booking flow while testing keyboard access, semantic markup, labels, focus order, and understandable status feedback. React does not replace browser accessibility rules, so verify the generated interface.
Example 9: State ownership check
For the Support ticket, identify which component truly owns the information involved in Reusable UI Primitives. Remove duplicated state and derive values during rendering when they can be calculated from existing props or state. Reusable UI Primitives is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 10: Network-delay scenario
Assume the Lesson tracker is waiting on a slow API while using Reusable UI Primitives. Decide what stays interactive, what shows pending feedback, what can be cancelled, and how stale responses are prevented from replacing newer data.
React coding example
export default function TopicDemo() {
return (
<section aria-labelledby="topic-title" className="topic-panel">
<h2 id="topic-title">{"Reusable UI Primitives"}</h2>
<label>
Search
<input name="search" autoComplete="off" />
</label>
<button type="button">Apply</button>
</section>
);
}Step-by-step code explanation
- Identify the responsibility demonstrated by Reusable UI Primitives.
- Read the component from inputs to returned JSX before focusing on individual syntax.
- Trace which event, prop, promise, or state update can cause the visible result to change.
- Test one normal path and one edge case so the behavior is not inferred from the happy path alone.
- Keep the example small enough that you can explain every render and every external side effect.
Expected behavior: A small React interface demonstrating Reusable UI Primitives; the exact browser text depends on the interaction or data used in the example.
Practice exercise
Create a small interface focused on Reusable UI Primitives. Write the expected screen state before running it, test one edge case, and change one input or interaction. Then explain which component owns the relevant data, what caused the render, and one accessibility or small-screen check you would perform before shipping the feature. Record the result as the Chapter 43 practice for CSS Modules and Design Systems.
43.5 Theme Architecture
Theme Architecture is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs. In Chapter 43, the purpose is to make the behavior observable rather than memorizing an API. Follow the value from its source through the component tree and identify what React needs in order to produce the next interface. This section 43.5 connects the idea directly to CSS Modules and Design Systems.
For Theme Architecture, inspect inputs, component ownership, visible output, edge cases, and the reason another render occurs. A reliable React design makes ownership explicit, keeps rendering predictable, and separates calculations from synchronization with external systems. When a feature seems complicated, reduce it to one component, one state change, or one boundary and rebuild from that verified behavior. In CSS Modules and Design Systems, keep the Theme Architecture responsibility visible while you test it.
This topic emphasizes production behavior. Use complete states for loading, success, empty data, and failure when those states can occur. After the example works, explain why React rendered what you see and which change would cause another render; that reasoning is more valuable than copying syntax. For section 43.5, relate that explanation back to Theme Architecture.
Key terms in plain language
- Interface contract — the behavior users and other components can rely on.
- Theme — a focused part of theme architecture used to describe one responsibility, input, rendering decision, or boundary in the interface.
- Architecture — a focused part of theme architecture used to describe one responsibility, input, rendering decision, or boundary in the interface.
10 teaching examples
Example 1: Performance experiment
Profile the Dashboard filter before optimizing Theme Architecture. Record which components render, what calculation is costly, and whether the delay is actually noticeable; apply an optimization only when the measurement supports it. Theme Architecture is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 2: Production review
Assume the Message composer feature using Theme Architecture ships to many devices and languages. Review error recovery, loading states, accessibility, RTL layout, small-screen width, security boundaries, and whether monitoring can reveal failures.
Example 3: Smallest useful case
Create the smallest working version of Theme Architecture inside a Analytics card. Keep one input and one visible result, then describe inputs, component ownership, visible output, edge cases, and the reason another render occurs. This gives you a baseline before extra features hide the important behavior. Theme Architecture is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 4: Change one input
Keep the Booking flow example stable but change one input that affects Theme Architecture. Predict what React will render before running the code, then compare the result with your prediction and explain the render path.
Example 5: Two-component comparison
Build one version of the Support ticket with the Theme Architecture responsibility in the parent and another with it in the child. Compare data ownership, reuse, and how many components need to know about the decision. Theme Architecture is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 6: Failure or edge case
Create a safe edge case for Theme Architecture in the Lesson tracker: empty data, a missing prop, a rejected request, rapid clicks, or an unmounted element. Show the user a clear state instead of allowing confusing or stale output.
Example 7: Accessibility check
Use Theme Architecture in the Course catalog while testing keyboard access, semantic markup, labels, focus order, and understandable status feedback. React does not replace browser accessibility rules, so verify the generated interface.
Example 8: State ownership check
For the Profile settings, identify which component truly owns the information involved in Theme Architecture. Remove duplicated state and derive values during rendering when they can be calculated from existing props or state. Theme Architecture is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
Example 9: Network-delay scenario
Assume the Search panel is waiting on a slow API while using Theme Architecture. Decide what stays interactive, what shows pending feedback, what can be cancelled, and how stale responses are prevented from replacing newer data.
Example 10: Refactoring exercise
Take a large Shopping cart component that mixes Theme Architecture with unrelated concerns. Extract one focused component or custom hook, give it a narrow API, and confirm that the user-visible behavior stays the same.
React coding example
export default function TopicDemo() {
return (
<section aria-labelledby="topic-title" className="topic-panel">
<h2 id="topic-title">{"Theme Architecture"}</h2>
<label>
Search
<input name="search" autoComplete="off" />
</label>
<button type="button">Apply</button>
</section>
);
}Step-by-step code explanation
- Identify the responsibility demonstrated by Theme Architecture.
- Read the component from inputs to returned JSX before focusing on individual syntax.
- Trace which event, prop, promise, or state update can cause the visible result to change.
- Test one normal path and one edge case so the behavior is not inferred from the happy path alone.
- Keep the example small enough that you can explain every render and every external side effect.
Expected behavior: A small React interface demonstrating Theme Architecture; the exact browser text depends on the interaction or data used in the example.
Practice exercise
Create a small interface focused on Theme Architecture. Write the expected screen state before running it, test one edge case, and change one input or interaction. Then explain which component owns the relevant data, what caused the render, and one accessibility or small-screen check you would perform before shipping the feature. Record the result as the Chapter 43 practice for CSS Modules and Design Systems.
Chapter 43 review — 20 questions and answers
1. What problem does CSS Module Basics help solve in this chapter?
Answer: CSS Module Basics is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
2. What should you inspect when CSS Module Basics does not behave as expected?
Answer: Check inputs, component ownership, visible output, edge cases, and the reason another render occurs. Reduce the example until you can identify the input, render decision, update, and visible result.
3. How can you practice CSS Module Basics without copying a large application?
Answer: Build a small component focused on CSS Module Basics, predict its output, change one condition, and explain why React renders the new result.
4. What production concern belongs with CSS Module Basics?
Answer: Review error recovery, accessibility, performance, security boundaries, localization, and small-screen behavior according to what CSS Module Basics touches.
5. What problem does Scoped Class Names help solve in this chapter?
Answer: Scoped Class Names is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
6. What should you inspect when Scoped Class Names does not behave as expected?
Answer: Check inputs, component ownership, visible output, edge cases, and the reason another render occurs. Reduce the example until you can identify the input, render decision, update, and visible result.
7. How can you practice Scoped Class Names without copying a large application?
Answer: Build a small component focused on Scoped Class Names, predict its output, change one condition, and explain why React renders the new result.
8. What production concern belongs with Scoped Class Names?
Answer: Review error recovery, accessibility, performance, security boundaries, localization, and small-screen behavior according to what Scoped Class Names touches.
9. What problem does Design Tokens help solve in this chapter?
Answer: Design Tokens is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
10. What should you inspect when Design Tokens does not behave as expected?
Answer: Check trust boundaries, server verification, token exposure, unsafe HTML, and authorization decisions. Reduce the example until you can identify the input, render decision, update, and visible result.
11. How can you practice Design Tokens without copying a large application?
Answer: Build a small component focused on Design Tokens, predict its output, change one condition, and explain why React renders the new result.
12. What production concern belongs with Design Tokens?
Answer: Review error recovery, accessibility, performance, security boundaries, localization, and small-screen behavior according to what Design Tokens touches.
13. What problem does Reusable UI Primitives help solve in this chapter?
Answer: Reusable UI Primitives is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
14. What should you inspect when Reusable UI Primitives does not behave as expected?
Answer: Check inputs, component ownership, visible output, edge cases, and the reason another render occurs. Reduce the example until you can identify the input, render decision, update, and visible result.
15. How can you practice Reusable UI Primitives without copying a large application?
Answer: Build a small component focused on Reusable UI Primitives, predict its output, change one condition, and explain why React renders the new result.
16. What production concern belongs with Reusable UI Primitives?
Answer: Review error recovery, accessibility, performance, security boundaries, localization, and small-screen behavior according to what Reusable UI Primitives touches.
17. What problem does Theme Architecture help solve in this chapter?
Answer: Theme Architecture is best understood through interface contract: the behavior users and other components can rely on. Focus on accessibility, styling boundaries, testing, types, and stable reusable APIs.
18. What should you inspect when Theme Architecture does not behave as expected?
Answer: Check inputs, component ownership, visible output, edge cases, and the reason another render occurs. Reduce the example until you can identify the input, render decision, update, and visible result.
19. How can you practice Theme Architecture without copying a large application?
Answer: Build a small component focused on Theme Architecture, predict its output, change one condition, and explain why React renders the new result.
20. What production concern belongs with Theme Architecture?
Answer: Review error recovery, accessibility, performance, security boundaries, localization, and small-screen behavior according to what Theme Architecture touches.