CSS • Chapter 42 • Foundations to Production
Feature Queries
Every topic includes a CSS/HTML coding example, ten focused teaching examples, code explanation, expected result, practice, and responsive/translated-layout checks.
42.1 @supports Basics
@supports Basics is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size. The goal is to connect the syntax to the browser's layout and cascade decisions rather than memorize a property name.
For @supports Basics in Chapter 42, inspect the matched selector, computed value, containing block or formatting context, intrinsic size, and any min/max constraints. When translation is enabled, also inspect whether longer text or RTL direction changes the available inline space.
Start with one small example for @supports Basics, resize the viewport, increase text size, translate the label, and add a competing rule. This shows whether the technique remains predictable under real content rather than only in a fixed desktop mockup. This explanation is specific to Chapter 42, topic 1.
Concept in plain language
@supports Basics is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size.
10 teaching examples
Example 1: Smallest useful case
Build a minimal media player for @supports Basics. Keep only the declarations needed to see the behavior clearly, then inspect the computed styles. Chapter 42, topic 1, example 1.
Example 2: Change one value
Change one important CSS value in the notification example for @supports Basics. Predict the visual difference before reloading the page. Chapter 42, topic 1, example 2.
Example 3: Narrow-screen test
Test @supports Basics in the language selector at 320px, 375px, and tablet width. Watch for min-content sizing, unwrapped text, and elements that refuse to shrink. Chapter 42, topic 1, example 3.
Example 4: Translated-text test
Translate the course card into a language with longer labels while using @supports Basics. Confirm buttons, headings, and navigation wrap without widening the page. Chapter 42, topic 1, example 4.
Example 5: Arabic/Persian test
Switch the navigation bar to Arabic or Persian. Verify logical spacing, start/end alignment, sidebar direction, and LTR code islands. Chapter 42, topic 1, example 5.
Example 6: Accessibility test
Check @supports Basics in the article with keyboard focus, zoom, reduced motion, forced colors, and high text scaling where relevant. Chapter 42, topic 1, example 6.
Example 7: Cascade test
Add a competing rule to the profile panel and determine why the declaration for @supports Basics wins or loses using the browser's Styles and Computed panels. Chapter 42, topic 1, example 7.
Example 8: Content-stress test
Fill the search form with very long words, URLs, translated text, images, and nested controls. Adjust @supports Basics without hiding meaningful content. Chapter 42, topic 1, example 8.
Example 9: Refactoring test
Rewrite the dashboard so @supports Basics uses reusable tokens, logical properties, or a component class while preserving the same behavior. Chapter 42, topic 1, example 9.
Example 10: Production review
Review @supports Basics in the photo gallery for browser support, fallback behavior, RTL, small screens, print, motion preferences, and maintainability. Chapter 42, topic 1, example 10.
CSS/HTML coding example
<!-- HTML -->
<div class="layout">Feature query</div>
<style>
@supports (display:grid) { .layout { display:grid; } }
</style>Step-by-step code explanation
- Identify the selector and declaration that demonstrate @supports Basics.
- Read the HTML structure first so you know which box or relationship the CSS is styling.
- @supports conditionally applies CSS when the tested feature is supported.
- Resize the viewport and test long translated content. Confirm that flex/grid items use min-width:0 where needed and that only code or genuinely wide content scrolls locally.
- Switch to Arabic or Persian and verify logical start/end spacing, text alignment, sidebar direction, and LTR isolation for code.
Expected result: The browser visibly demonstrates @supports Basics without requiring the page to exceed the viewport width. If the example contains wide code, only the code block scrolls horizontally. This expected result belongs to Chapter 42, topic 1.
Practice exercise
Build a fresh example for @supports Basics from Chapter 42. Change one value, inspect the computed styles, test at 320px and tablet width, translate the visible text, switch the page to RTL, and explain why the final declaration or layout behavior occurs.
42.2 Testing Property Values
Testing Property Values is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size. The goal is to connect the syntax to the browser's layout and cascade decisions rather than memorize a property name.
For Testing Property Values in Chapter 42, inspect the matched selector, computed value, containing block or formatting context, intrinsic size, and any min/max constraints. When translation is enabled, also inspect whether longer text or RTL direction changes the available inline space.
Start with one small example for Testing Property Values, resize the viewport, increase text size, translate the label, and add a competing rule. This shows whether the technique remains predictable under real content rather than only in a fixed desktop mockup. This explanation is specific to Chapter 42, topic 2.
Concept in plain language
Testing Property Values is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size.
10 teaching examples
Example 1: Smallest useful case
Build a minimal course card for Testing Property Values. Keep only the declarations needed to see the behavior clearly, then inspect the computed styles. Chapter 42, topic 2, example 1.
Example 2: Change one value
Change one important CSS value in the navigation bar example for Testing Property Values. Predict the visual difference before reloading the page. Chapter 42, topic 2, example 2.
Example 3: Narrow-screen test
Test Testing Property Values in the article at 320px, 375px, and tablet width. Watch for min-content sizing, unwrapped text, and elements that refuse to shrink. Chapter 42, topic 2, example 3.
Example 4: Translated-text test
Translate the profile panel into a language with longer labels while using Testing Property Values. Confirm buttons, headings, and navigation wrap without widening the page. Chapter 42, topic 2, example 4.
Example 5: Arabic/Persian test
Switch the search form to Arabic or Persian. Verify logical spacing, start/end alignment, sidebar direction, and LTR code islands. Chapter 42, topic 2, example 5.
Example 6: Accessibility test
Check Testing Property Values in the dashboard with keyboard focus, zoom, reduced motion, forced colors, and high text scaling where relevant. Chapter 42, topic 2, example 6.
Example 7: Cascade test
Add a competing rule to the photo gallery and determine why the declaration for Testing Property Values wins or loses using the browser's Styles and Computed panels. Chapter 42, topic 2, example 7.
Example 8: Content-stress test
Fill the pricing table with very long words, URLs, translated text, images, and nested controls. Adjust Testing Property Values without hiding meaningful content. Chapter 42, topic 2, example 8.
Example 9: Refactoring test
Rewrite the lesson sidebar so Testing Property Values uses reusable tokens, logical properties, or a component class while preserving the same behavior. Chapter 42, topic 2, example 9.
Example 10: Production review
Review Testing Property Values in the contact form for browser support, fallback behavior, RTL, small screens, print, motion preferences, and maintainability. Chapter 42, topic 2, example 10.
CSS/HTML coding example
<!-- HTML -->
<div class="demo testing-property-values">CSS topic: Testing Property Values</div>
<style>
.testing-property-values {
padding: 1rem;
border: 1px solid #94a3b8;
}
</style>Step-by-step code explanation
- Identify the selector and declaration that demonstrate Testing Property Values.
- Read the HTML structure first so you know which box or relationship the CSS is styling.
- The selector targets the demonstration for Testing Property Values, and the declaration changes a visible part of its presentation.
- Resize the viewport and test long translated content. Confirm that flex/grid items use min-width:0 where needed and that only code or genuinely wide content scrolls locally.
- Switch to Arabic or Persian and verify logical start/end spacing, text alignment, sidebar direction, and LTR isolation for code.
Expected result: The browser visibly demonstrates Testing Property Values without requiring the page to exceed the viewport width. If the example contains wide code, only the code block scrolls horizontally. This expected result belongs to Chapter 42, topic 2.
Practice exercise
Build a fresh example for Testing Property Values from Chapter 42. Change one value, inspect the computed styles, test at 320px and tablet width, translate the visible text, switch the page to RTL, and explain why the final declaration or layout behavior occurs.
42.3 not in supports
not in supports is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size. The goal is to connect the syntax to the browser's layout and cascade decisions rather than memorize a property name.
For not in supports in Chapter 42, inspect the matched selector, computed value, containing block or formatting context, intrinsic size, and any min/max constraints. When translation is enabled, also inspect whether longer text or RTL direction changes the available inline space.
Start with one small example for not in supports, resize the viewport, increase text size, translate the label, and add a competing rule. This shows whether the technique remains predictable under real content rather than only in a fixed desktop mockup. This explanation is specific to Chapter 42, topic 3.
Concept in plain language
not in supports is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size.
10 teaching examples
Example 1: Smallest useful case
Build a minimal profile panel for not in supports. Keep only the declarations needed to see the behavior clearly, then inspect the computed styles. Chapter 42, topic 3, example 1.
Example 2: Change one value
Change one important CSS value in the search form example for not in supports. Predict the visual difference before reloading the page. Chapter 42, topic 3, example 2.
Example 3: Narrow-screen test
Test not in supports in the dashboard at 320px, 375px, and tablet width. Watch for min-content sizing, unwrapped text, and elements that refuse to shrink. Chapter 42, topic 3, example 3.
Example 4: Translated-text test
Translate the photo gallery into a language with longer labels while using not in supports. Confirm buttons, headings, and navigation wrap without widening the page. Chapter 42, topic 3, example 4.
Example 5: Arabic/Persian test
Switch the pricing table to Arabic or Persian. Verify logical spacing, start/end alignment, sidebar direction, and LTR code islands. Chapter 42, topic 3, example 5.
Example 6: Accessibility test
Check not in supports in the lesson sidebar with keyboard focus, zoom, reduced motion, forced colors, and high text scaling where relevant. Chapter 42, topic 3, example 6.
Example 7: Cascade test
Add a competing rule to the contact form and determine why the declaration for not in supports wins or loses using the browser's Styles and Computed panels. Chapter 42, topic 3, example 7.
Example 8: Content-stress test
Fill the button group with very long words, URLs, translated text, images, and nested controls. Adjust not in supports without hiding meaningful content. Chapter 42, topic 3, example 8.
Example 9: Refactoring test
Rewrite the data table so not in supports uses reusable tokens, logical properties, or a component class while preserving the same behavior. Chapter 42, topic 3, example 9.
Example 10: Production review
Review not in supports in the media player for browser support, fallback behavior, RTL, small screens, print, motion preferences, and maintainability. Chapter 42, topic 3, example 10.
CSS/HTML coding example
<!-- HTML -->
<article class="card">Normal</article><article class="card featured">Featured</article>
<style>
.card:not(.featured) { opacity: .75; }
</style>Step-by-step code explanation
- Identify the selector and declaration that demonstrate not in supports.
- Read the HTML structure first so you know which box or relationship the CSS is styling.
- :not() excludes matching elements.
- Resize the viewport and test long translated content. Confirm that flex/grid items use min-width:0 where needed and that only code or genuinely wide content scrolls locally.
- Switch to Arabic or Persian and verify logical start/end spacing, text alignment, sidebar direction, and LTR isolation for code.
Expected result: The browser visibly demonstrates not in supports without requiring the page to exceed the viewport width. If the example contains wide code, only the code block scrolls horizontally. This expected result belongs to Chapter 42, topic 3.
Practice exercise
Build a fresh example for not in supports from Chapter 42. Change one value, inspect the computed styles, test at 320px and tablet width, translate the visible text, switch the page to RTL, and explain why the final declaration or layout behavior occurs.
42.4 Combining Support Conditions
Combining Support Conditions is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size. The goal is to connect the syntax to the browser's layout and cascade decisions rather than memorize a property name.
For Combining Support Conditions in Chapter 42, inspect the matched selector, computed value, containing block or formatting context, intrinsic size, and any min/max constraints. When translation is enabled, also inspect whether longer text or RTL direction changes the available inline space.
Start with one small example for Combining Support Conditions, resize the viewport, increase text size, translate the label, and add a competing rule. This shows whether the technique remains predictable under real content rather than only in a fixed desktop mockup. This explanation is specific to Chapter 42, topic 4.
Concept in plain language
Combining Support Conditions is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size.
10 teaching examples
Example 1: Smallest useful case
Build a minimal photo gallery for Combining Support Conditions. Keep only the declarations needed to see the behavior clearly, then inspect the computed styles. Chapter 42, topic 4, example 1.
Example 2: Change one value
Change one important CSS value in the pricing table example for Combining Support Conditions. Predict the visual difference before reloading the page. Chapter 42, topic 4, example 2.
Example 3: Narrow-screen test
Test Combining Support Conditions in the lesson sidebar at 320px, 375px, and tablet width. Watch for min-content sizing, unwrapped text, and elements that refuse to shrink. Chapter 42, topic 4, example 3.
Example 4: Translated-text test
Translate the contact form into a language with longer labels while using Combining Support Conditions. Confirm buttons, headings, and navigation wrap without widening the page. Chapter 42, topic 4, example 4.
Example 5: Arabic/Persian test
Switch the button group to Arabic or Persian. Verify logical spacing, start/end alignment, sidebar direction, and LTR code islands. Chapter 42, topic 4, example 5.
Example 6: Accessibility test
Check Combining Support Conditions in the data table with keyboard focus, zoom, reduced motion, forced colors, and high text scaling where relevant. Chapter 42, topic 4, example 6.
Example 7: Cascade test
Add a competing rule to the media player and determine why the declaration for Combining Support Conditions wins or loses using the browser's Styles and Computed panels. Chapter 42, topic 4, example 7.
Example 8: Content-stress test
Fill the notification with very long words, URLs, translated text, images, and nested controls. Adjust Combining Support Conditions without hiding meaningful content. Chapter 42, topic 4, example 8.
Example 9: Refactoring test
Rewrite the language selector so Combining Support Conditions uses reusable tokens, logical properties, or a component class while preserving the same behavior. Chapter 42, topic 4, example 9.
Example 10: Production review
Review Combining Support Conditions in the course card for browser support, fallback behavior, RTL, small screens, print, motion preferences, and maintainability. Chapter 42, topic 4, example 10.
CSS/HTML coding example
<!-- HTML -->
<div class="demo combining-support-conditions">CSS topic: Combining Support Conditions</div>
<style>
.combining-support-conditions {
padding: 1rem;
border: 1px solid #94a3b8;
}
</style>Step-by-step code explanation
- Identify the selector and declaration that demonstrate Combining Support Conditions.
- Read the HTML structure first so you know which box or relationship the CSS is styling.
- The selector targets the demonstration for Combining Support Conditions, and the declaration changes a visible part of its presentation.
- Resize the viewport and test long translated content. Confirm that flex/grid items use min-width:0 where needed and that only code or genuinely wide content scrolls locally.
- Switch to Arabic or Persian and verify logical start/end spacing, text alignment, sidebar direction, and LTR isolation for code.
Expected result: The browser visibly demonstrates Combining Support Conditions without requiring the page to exceed the viewport width. If the example contains wide code, only the code block scrolls horizontally. This expected result belongs to Chapter 42, topic 4.
Practice exercise
Build a fresh example for Combining Support Conditions from Chapter 42. Change one value, inspect the computed styles, test at 320px and tablet width, translate the visible text, switch the page to RTL, and explain why the final declaration or layout behavior occurs.
42.5 Progressive Enhancement
Progressive Enhancement is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size. The goal is to connect the syntax to the browser's layout and cascade decisions rather than memorize a property name.
For Progressive Enhancement in Chapter 42, inspect the matched selector, computed value, containing block or formatting context, intrinsic size, and any min/max constraints. When translation is enabled, also inspect whether longer text or RTL direction changes the available inline space.
Start with one small example for Progressive Enhancement, resize the viewport, increase text size, translate the label, and add a competing rule. This shows whether the technique remains predictable under real content rather than only in a fixed desktop mockup. This explanation is specific to Chapter 42, topic 5.
Concept in plain language
Progressive Enhancement is part of the CSS system covered in Chapter 42. The key is to understand what box, selector, cascade rule, layout algorithm, or user preference the declaration affects, then test the result at more than one viewport size.
10 teaching examples
Example 1: Smallest useful case
Build a minimal contact form for Progressive Enhancement. Keep only the declarations needed to see the behavior clearly, then inspect the computed styles. Chapter 42, topic 5, example 1.
Example 2: Change one value
Change one important CSS value in the button group example for Progressive Enhancement. Predict the visual difference before reloading the page. Chapter 42, topic 5, example 2.
Example 3: Narrow-screen test
Test Progressive Enhancement in the data table at 320px, 375px, and tablet width. Watch for min-content sizing, unwrapped text, and elements that refuse to shrink. Chapter 42, topic 5, example 3.
Example 4: Translated-text test
Translate the media player into a language with longer labels while using Progressive Enhancement. Confirm buttons, headings, and navigation wrap without widening the page. Chapter 42, topic 5, example 4.
Example 5: Arabic/Persian test
Switch the notification to Arabic or Persian. Verify logical spacing, start/end alignment, sidebar direction, and LTR code islands. Chapter 42, topic 5, example 5.
Example 6: Accessibility test
Check Progressive Enhancement in the language selector with keyboard focus, zoom, reduced motion, forced colors, and high text scaling where relevant. Chapter 42, topic 5, example 6.
Example 7: Cascade test
Add a competing rule to the course card and determine why the declaration for Progressive Enhancement wins or loses using the browser's Styles and Computed panels. Chapter 42, topic 5, example 7.
Example 8: Content-stress test
Fill the navigation bar with very long words, URLs, translated text, images, and nested controls. Adjust Progressive Enhancement without hiding meaningful content. Chapter 42, topic 5, example 8.
Example 9: Refactoring test
Rewrite the article so Progressive Enhancement uses reusable tokens, logical properties, or a component class while preserving the same behavior. Chapter 42, topic 5, example 9.
Example 10: Production review
Review Progressive Enhancement in the profile panel for browser support, fallback behavior, RTL, small screens, print, motion preferences, and maintainability. Chapter 42, topic 5, example 10.
CSS/HTML coding example
<!-- HTML -->
<div class="demo progressive-enhancement">CSS topic: Progressive Enhancement</div>
<style>
.progressive-enhancement {
padding: 1rem;
border: 1px solid #94a3b8;
}
</style>Step-by-step code explanation
- Identify the selector and declaration that demonstrate Progressive Enhancement.
- Read the HTML structure first so you know which box or relationship the CSS is styling.
- The selector targets the demonstration for Progressive Enhancement, and the declaration changes a visible part of its presentation.
- Resize the viewport and test long translated content. Confirm that flex/grid items use min-width:0 where needed and that only code or genuinely wide content scrolls locally.
- Switch to Arabic or Persian and verify logical start/end spacing, text alignment, sidebar direction, and LTR isolation for code.
Expected result: The browser visibly demonstrates Progressive Enhancement without requiring the page to exceed the viewport width. If the example contains wide code, only the code block scrolls horizontally. This expected result belongs to Chapter 42, topic 5.
Practice exercise
Build a fresh example for Progressive Enhancement from Chapter 42. Change one value, inspect the computed styles, test at 320px and tablet width, translate the visible text, switch the page to RTL, and explain why the final declaration or layout behavior occurs.
Chapter 42 review — 10 questions and answers
1. What should you inspect first when @supports Basics does not work as expected?
Answer: Inspect the matched rules, computed value, box size, layout context, and inherited values for @supports Basics. Then reduce the example until the winning declaration is clear.
2. How should @supports Basics be checked before publishing?
Answer: Test @supports Basics on narrow and wide screens, with long translated text, at increased zoom, and in RTL where direction can affect layout. Add a fallback if browser support or user preferences require one.
3. What should you inspect first when Testing Property Values does not work as expected?
Answer: Inspect the matched rules, computed value, box size, layout context, and inherited values for Testing Property Values. Then reduce the example until the winning declaration is clear.
4. How should Testing Property Values be checked before publishing?
Answer: Test Testing Property Values on narrow and wide screens, with long translated text, at increased zoom, and in RTL where direction can affect layout. Add a fallback if browser support or user preferences require one.
5. What should you inspect first when not in supports does not work as expected?
Answer: Inspect the matched rules, computed value, box size, layout context, and inherited values for not in supports. Then reduce the example until the winning declaration is clear.
6. How should not in supports be checked before publishing?
Answer: Test not in supports on narrow and wide screens, with long translated text, at increased zoom, and in RTL where direction can affect layout. Add a fallback if browser support or user preferences require one.
7. What should you inspect first when Combining Support Conditions does not work as expected?
Answer: Inspect the matched rules, computed value, box size, layout context, and inherited values for Combining Support Conditions. Then reduce the example until the winning declaration is clear.
8. How should Combining Support Conditions be checked before publishing?
Answer: Test Combining Support Conditions on narrow and wide screens, with long translated text, at increased zoom, and in RTL where direction can affect layout. Add a fallback if browser support or user preferences require one.
9. What should you inspect first when Progressive Enhancement does not work as expected?
Answer: Inspect the matched rules, computed value, box size, layout context, and inherited values for Progressive Enhancement. Then reduce the example until the winning declaration is clear.
10. How should Progressive Enhancement be checked before publishing?
Answer: Test Progressive Enhancement on narrow and wide screens, with long translated text, at increased zoom, and in RTL where direction can affect layout. Add a fallback if browser support or user preferences require one.