Placeholder selectors with % in SASS - Mini Project: Build & Apply

Building a Button Style with Sass Placeholder Selectors

📖 Scenario: You are creating a website with buttons that share common styles. To keep your CSS clean and avoid repeating code, you will use Sass placeholder selectors. These placeholders let you write styles once and reuse them in different button classes.

🎯 Goal: Build a Sass file that defines a placeholder selector for button styles, then create two button classes that reuse this placeholder. This will produce consistent button styles with minimal repeated code.

📋 What You'll Learn

Create a Sass placeholder selector named %button-style with padding and border radius.

Create a variable $primary-color with the value #3498db.

Create a class .btn-primary that uses %button-style and sets the background color to $primary-color.

Create a class .btn-secondary that uses %button-style and sets the background color to #95a5a6.

💡 Why This Matters

🌍 Real World

Web developers often need to style multiple buttons or components with shared styles. Using Sass placeholders helps write cleaner, reusable CSS.

💼 Career

Knowing how to use Sass placeholders and variables is a valuable skill for front-end developers to write maintainable and scalable stylesheets.

1

Create the placeholder selector %button-style

Write a Sass placeholder selector called %button-style that sets padding to 1rem 2rem and border-radius to 0.5rem.

SASS

// Your code here

Hint

Use %button-style followed by curly braces and add the padding and border-radius inside.

2

Create the variable $primary-color

Add a Sass variable named $primary-color and set it to the color #3498db.

SASS

%button-style {
  padding: 1rem 2rem;
  border-radius: 0.5rem;
}

// Your code here

Hint

Use $primary-color: #3498db; to create the variable.

3

Create the .btn-primary class using the placeholder

Write a Sass class called .btn-primary that @extends the %button-style placeholder and sets background-color to $primary-color.

SASS

%button-style {
  padding: 1rem 2rem;
  border-radius: 0.5rem;
}

$primary-color: #3498db;

// Your code here

Hint

Use @extend %button-style; inside .btn-primary and set the background color to $primary-color.

4

Create the .btn-secondary class using the placeholder

Write a Sass class called .btn-secondary that @extends the %button-style placeholder and sets background-color to #95a5a6.

SASS

%button-style {
  padding: 1rem 2rem;
  border-radius: 0.5rem;
}

$primary-color: #3498db;

.btn-primary {
  @extend %button-style;
  background-color: $primary-color;
}

// Your code here

Hint

Use @extend %button-style; inside .btn-secondary and set the background color to #95a5a6.

Practice

1. What is the main purpose of a placeholder selector in Sass, which starts with %?

easy

A. To hold reusable styles that can be extended by other selectors

B. To create a new HTML element

C. To define a variable for colors

D. To write comments in Sass code

Solution

1. Step 1: Understand what placeholder selectors do

   Placeholder selectors start with % and are used to hold styles that are not output directly but can be reused.

2. Step 2: Identify their usage

   They are extended by other selectors using @extend to apply the stored styles without duplicating CSS.

3. Final Answer:

   To hold reusable styles that can be extended by other selectors -> Option A

4. Quick Check:

   Placeholder selectors = reusable styles [OK]

Hint: Remember % means reusable style block [OK]

Common Mistakes:

• Thinking % creates HTML elements
• Confusing % with variables
• Using % for comments

2. Which of the following is the correct syntax to extend a placeholder selector named %button-style inside a Sass rule?

easy

A. button { @include %button-style; }

B. button { extend %button-style; }

C. button { @extend %button-style; }

D. button { %button-style; }

Solution

1. Step 1: Recall the syntax for extending placeholders

   In Sass, to apply styles from a placeholder, you use @extend %placeholder-name; inside a selector.

2. Step 2: Check each option

   button { @extend %button-style; } uses @extend %button-style; correctly. The other options use incorrect keywords or syntax.

3. Final Answer:

   button { @extend %button-style; } -> Option C

4. Quick Check:

   @extend %placeholder-name; = correct syntax [OK]

Hint: Use @extend with % to reuse styles [OK]

Common Mistakes:

• Using @include instead of @extend
• Omitting the @ symbol
• Writing %button-style without @extend

3. Given the Sass code:

%alert { color: red; font-weight: bold; }
.warning { @extend %alert; background: yellow; }

What CSS will be generated?

medium

A. %alert { color: red; font-weight: bold; }
.warning { background: yellow; }

B. .alert, .warning { color: red; font-weight: bold; background: yellow; }

C. .warning { background: yellow; }
%alert { color: red; font-weight: bold; }

D. .warning { color: red; font-weight: bold; background: yellow; }

Solution

1. Step 1: Understand placeholder output

   Placeholder selectors do not output CSS themselves. Their styles are included only when extended.

2. Step 2: Analyze the @extend usage

   The .warning class extends %alert, so it gets the styles from %alert plus its own background style.

3. Final Answer:

   .warning { color: red; font-weight: bold; background: yellow; } -> Option D

4. Quick Check:

   Placeholder styles appear only in extended selectors [OK]

Hint: Placeholder styles appear only when extended [OK]

Common Mistakes:

• Expecting %alert to appear in CSS
• Thinking styles duplicate without extend
• Confusing @extend with @include

4. Identify the error in this Sass code:

%card-style {
  border: 1px solid black;
}
.card {
  extend %card-style;
  padding: 1rem;
}

medium

A. Padding property is not allowed here

B. Missing @ symbol before extend

C. Placeholder selector name is invalid

D. Border property should be inside .card, not %card-style

Solution

1. Step 1: Check the syntax of @extend

   The correct syntax requires the @ symbol before extend to work properly.

2. Step 2: Identify the error in the code

   The code uses extend %card-style; without @, causing a syntax error.

3. Final Answer:

   Missing @ symbol before extend -> Option B

4. Quick Check:

   @extend must have @ symbol [OK]

Hint: Always use @ before extend keyword [OK]

Common Mistakes:

• Omitting @ before extend
• Misnaming placeholder selectors
• Misplacing properties inside placeholders

5. You want to create two button styles, .primary-btn and .secondary-btn, sharing common styles but with different colors. Which Sass code correctly uses placeholder selectors to avoid repeating common styles?

hard

A. %btn-common {
padding: 1rem;
border-radius: 0.5rem;
}
.primary-btn {
@extend %btn-common;
background-color: blue;
color: white;
}
.secondary-btn {
@extend %btn-common;
background-color: gray;
color: black;
}

B. .btn-common {
padding: 1rem;
border-radius: 0.5rem;
}
.primary-btn {
@extend .btn-common;
background-color: blue;
color: white;
}
.secondary-btn {
@extend .btn-common;
background-color: gray;
color: black;
}

C. %btn-common {
padding: 1rem;
border-radius: 0.5rem;
background-color: blue;
}
.primary-btn {
@extend %btn-common;
color: white;
}
.secondary-btn {
@extend %btn-common;
background-color: gray;
color: black;
}

D. %btn-common {
padding: 1rem;
border-radius: 0.5rem;
}
.primary-btn {
background-color: blue;
color: white;
}
.secondary-btn {
background-color: gray;
color: black;
}

Solution

1. Step 1: Identify the correct use of placeholder selectors

   Placeholder selectors start with % and hold common styles to be extended by other selectors.

2. Step 2: Check each option for correct reuse and color overrides

   %btn-common {
     padding: 1rem;
     border-radius: 0.5rem;
   }
   .primary-btn {
     @extend %btn-common;
     background-color: blue;
     color: white;
   }
   .secondary-btn {
     @extend %btn-common;
     background-color: gray;
     color: black;
   }

   correctly defines %btn-common with shared styles and extends it in both buttons, adding different colors separately.

   .btn-common {
     padding: 1rem;
     border-radius: 0.5rem;
   }
   .primary-btn {
     @extend .btn-common;
     background-color: blue;
     color: white;
   }
   .secondary-btn {
     @extend .btn-common;
     background-color: gray;
     color: black;
   }

   incorrectly uses a class instead of a placeholder.

   %btn-common {
     padding: 1rem;
     border-radius: 0.5rem;
     background-color: blue;
   }
   .primary-btn {
     @extend %btn-common;
     color: white;
   }
   .secondary-btn {
     @extend %btn-common;
     background-color: gray;
     color: black;
   }

   mixes shared and specific colors in the placeholder, causing unwanted style inheritance.

   %btn-common {
     padding: 1rem;
     border-radius: 0.5rem;
   }
   .primary-btn {
     background-color: blue;
     color: white;
   }
   .secondary-btn {
     background-color: gray;
     color: black;
   }

   does not use placeholders at all, repeating styles.

3. Final Answer:

   %btn-common placeholder with @extend usage in both buttons -> Option A

4. Quick Check:

   Use %placeholder for shared styles, extend and override colors [OK]

Hint: Put shared styles in %placeholder, extend, then add unique styles [OK]

Common Mistakes:

• Using classes instead of placeholders for shared styles
• Putting unique styles inside the placeholder
• Not using @extend to reuse styles