@extend directive in SASS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the @extend directive do in Sass?

The @extend directive lets one CSS selector inherit the styles of another selector. It helps avoid repeating the same styles.

beginner

How does @extend affect the compiled CSS output?

It combines selectors that share styles into one rule, reducing duplication and making CSS smaller and easier to maintain.

intermediate

Can @extend be used with placeholder selectors? What are placeholders?

Yes. Placeholders start with % and are not output alone in CSS. They are meant to be extended by other selectors.

intermediate

What happens if you @extend a selector inside a nested rule?

The extended styles are merged respecting the nesting, so the output CSS keeps the correct hierarchy and specificity.

advanced

Why should you be careful when using @extend with very generic selectors?

Because it can cause unexpected style merging and large combined selectors, making CSS harder to debug and maintain.

What symbol is used to define a placeholder selector in Sass?

A %

B @

C #

D $

Placeholder selectors start with % and are meant to be extended but do not output CSS on their own.

What is the main benefit of using @extend in Sass?

A To repeat styles multiple times

B To create animations

C To add JavaScript functionality

D To combine selectors and avoid style duplication

@extend helps combine selectors sharing styles, reducing repetition in the CSS output.

If you @extend a selector inside a nested rule, what happens?

A It causes a syntax error

B The styles are ignored

C The styles are merged respecting nesting

D It duplicates the styles

Sass merges extended selectors respecting nesting to keep correct CSS structure.

Which of these is a risk when overusing @extend with generic selectors?

A Unexpected style merging and complex selectors

B CSS file size increases

C JavaScript errors

D HTML validation errors

Using @extend with generic selectors can create large combined selectors that are hard to debug.

Can @extend be used to inherit styles from multiple selectors at once?

A Only with placeholders

B Yes, by listing selectors separated by commas

C No, only one selector at a time

D Only inside media queries

You can extend multiple selectors by listing them separated by commas in @extend.

Explain how the @extend directive works in Sass and why it is useful.

Think about how sharing styles can save writing the same CSS again.

Describe potential problems when using @extend with very generic selectors and how to avoid them.

Consider what happens if many selectors get combined unexpectedly.

Practice

1. What does the @extend directive do in Sass?

easy

A. It defines a variable.

B. It creates a new CSS property.

C. It imports external CSS files.

D. It allows one selector to reuse styles from another selector.

Solution

1. Step 1: Understand the purpose of @extend

   The @extend directive is used to share styles between selectors in Sass.

2. Step 2: Identify what @extend does

   It copies the styles of one selector into another, reducing repetition.

3. Final Answer:

   It allows one selector to reuse styles from another selector. -> Option D

4. Quick Check:

   @extend = reuse styles [OK]

Hint: Remember: @extend shares styles between selectors [OK]

Common Mistakes:

• Thinking @extend creates new properties
• Confusing @extend with imports
• Using @extend to define variables

2. Which of the following is the correct syntax to extend styles from .button to .submit in Sass?

easy

A. .submit { @extend .button; }

B. .submit { extend(@button); }

C. .submit { @extend .button(); }

D. .submit { @extend '#button'; }

Solution

1. Step 1: Recall correct @extend syntax

   The correct syntax is @extend followed by the selector name without quotes or parentheses.

2. Step 2: Check each option

   .submit { @extend .button; } uses @extend .button; which is correct. Others use wrong syntax like parentheses or quotes.

3. Final Answer:

   .submit { @extend .button; } -> Option A

4. Quick Check:

   Correct syntax = @extend .selector; [OK]

Hint: Use @extend followed by selector without quotes or parentheses [OK]

Common Mistakes:

• Adding parentheses after selector
• Using quotes around selector
• Using wrong function-like syntax

3. Given this Sass code:

.alert { color: red; font-weight: bold; }
.error { @extend .alert; }

What CSS will be generated?

medium

A. .alert { color: red; font-weight: bold; } .error { color: red; font-weight: bold; }

B. .alert, .error { color: red; font-weight: bold; }

C. .error { color: red; font-weight: bold; }

D. .alert { color: red; } .error { font-weight: bold; }

Solution

1. Step 1: Understand @extend output

   @extend merges selectors so they share the same style block.

2. Step 2: Apply to given code

   Both .alert and .error share the same styles in one combined selector.

3. Final Answer:

   .alert, .error { color: red; font-weight: bold; } -> Option B

4. Quick Check:

   Selectors combined with @extend [OK]

Hint: Remember: @extend combines selectors sharing styles [OK]

Common Mistakes:

• Expecting duplicated style blocks
• Thinking styles copy separately
• Splitting properties between selectors

4. What is wrong with this Sass code?

.card { border: 1px solid black; }
.panel { @extend card; }

medium

A. Missing dot before card in @extend selector.

B. Cannot use @extend inside .panel.

C. Border property is invalid.

D. No styles defined in .panel.

Solution

1. Step 1: Check @extend selector syntax

   The selector to extend must include the dot for class selectors.

2. Step 2: Identify error in code

   @extend card; misses the dot, should be @extend .card;.

3. Final Answer:

   Missing dot before card in @extend selector. -> Option A

4. Quick Check:

   Class selectors need dot in @extend [OK]

Hint: Always include dot for class names in @extend [OK]

Common Mistakes:

• Omitting dot before class name
• Thinking @extend can't be used inside rules
• Confusing property errors with selector errors

5. You want to create a .warning style that shares all styles from .alert but also adds background-color: yellow;. Which Sass code correctly does this?

hard

A. .warning { @extend alert; background-color: yellow; }

B. .warning { background-color: yellow; @extend .alert(); }

C. .warning { @extend .alert; background-color: yellow; }

D. .warning { @extend .alert background-color: yellow; }

Solution

1. Step 1: Understand @extend usage with additional styles

   You can use @extend inside a selector and add other properties after it.

2. Step 2: Check each option

   .warning { @extend .alert; background-color: yellow; } correctly uses @extend .alert; then adds background-color in the same block. Others have syntax errors: parentheses after selector, missing dot before alert, or missing semicolon.

3. Final Answer:

   .warning { @extend .alert; background-color: yellow; } -> Option C

4. Quick Check:

   @extend plus extra styles in same block [OK]

Hint: Put @extend first, then add extra styles in same block [OK]

Common Mistakes:

• Adding parentheses after selector
• Omitting dot before class name in @extend
• Missing semicolon after @extend