CSS basics · Lesson 9 of 12 · 7 minutes

CSS basics: Reusable utility classes

Small utility classes should have a predictable job and avoid accidental changes to unrelated components.

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Your objectives

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1
Build reusable utility classes
Build this first target: .stack with display: flex. Keep the selector relationships intact and inspect the preview.
Hint & worked example
Small utility classes should have a predictable job and avoid accidental changes to unrelated components.
The requested selectors and declarations exist outside comments.
```
.stack { display: flex; }
```
Common mistake to avoid: If the page fits one desktop viewport, no narrower viewport needs checking.
2
Extend the reusable utility classes example
Extend your file to include: .stack with display: flex; .stack with flex-direction: column. Keep the selector relationships intact and inspect the preview.
Hint & worked example
Small utility classes should have a predictable job and avoid accidental changes to unrelated components.
The requested selectors and declarations exist outside comments.
```
.stack { display: flex; }
.stack { flex-direction: column; }
```
Common mistake to avoid: Hiding all overflow always makes content accessible.
3
Verify the complete reusable utility classes pattern
Finish the pattern with: .stack with display: flex; .stack with flex-direction: column; .stack with gap: 1rem. Keep the selector relationships intact and inspect the preview.
Hint & worked example
Small utility classes should have a predictable job and avoid accidental changes to unrelated components.
The requested selectors and declarations exist outside comments.
```
.stack { display: flex; }
.stack { flex-direction: column; }
.stack { gap: 1rem; }
```
Common mistake to avoid: If the page fits one desktop viewport, no narrower viewport needs checking.

Understand the pattern

Small utility classes should have a predictable job and avoid accidental changes to unrelated components.

Misconceptions to reject

If the page fits one desktop viewport, no narrower viewport needs checking.
Hiding all overflow always makes content accessible.

The preview is a sanitized subset, not a full browser compatibility test.

Worked example and expected result

.stack { display: flex; }
.stack { flex-direction: column; }
.stack { gap: 1rem; }

Small utility classes should have a predictable job and avoid accidental changes to unrelated components.

Try a variation

Adapt the final example to a different project name while retaining its structure and relationships. A different context still needs a real browser and accessibility check.

Explain it

Which statement correctly explains reusable utility classes?If the page fits one desktop viewport, no narrower viewport needs checking.Hiding all overflow always makes content accessible.Small utility classes should have a predictable job and avoid accidental changes to unrelated components.

Apply it elsewhere

You reuse reusable utility classes in a different project. What must still be verified?Only whether the source code has the same number of lines.The resulting layout, focus behavior, and readability at the target viewport sizes.Nothing; passing a single exercise guarantees every future use.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

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