Variable scope in CSS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a CSS variable inside the :root selector.

CSS

:root {
  --main-color: [1];
}

Drag options to blanks, or click blank then click option'

Amain-color

B#3498db

Ccolor

Dvar(--main-color)

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable name as the value instead of a color.

Forgetting the '#' in the color code.

Using var(--main-color) when defining the variable.

The correct way to define a CSS variable is to assign a value like a color code. Here, #3498db is a valid color value.

2fill in blank

medium

Complete the code to use the CSS variable --main-color inside the body selector.

CSS

body {
  background-color: [1];
}

Drag options to blanks, or click blank then click option'

Avar(--main-color)

Bcolor(--main-color)

Cmain-color

D--main-color

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable name without var().

Using incorrect syntax like color(--main-color).

Forgetting the double dashes in the variable name.

To use a CSS variable, you must wrap its name with var(). So var(--main-color) correctly accesses the variable.

3fill in blank

hard

Fix the error in the code to correctly override the CSS variable --main-color inside the .button class.

CSS

.button {
  [1]: #e74c3c;
}

Drag options to blanks, or click blank then click option'

A--main-color

Bmain-color

Cvar(--main-color)

Dcolor

Attempts:

3 left

💡 Hint

Common Mistakes

Using var(--main-color) as a property name.

Using the variable name without dashes.

Using unrelated property names like color.

To override a CSS variable, you must use its full name with double dashes, like --main-color, not just the name or var().

4fill in blank

hard

Fill both blanks to define a CSS variable --text-size inside :root and use it in the p selector.

CSS

:root {
  [1]: 1.2rem;
}
p {
  font-size: [2];
}

Drag options to blanks, or click blank then click option'

A--text-size

Bvar(--text-size)

C--main-color

D1.2rem

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable name without dashes when defining.

Using the variable name without var() when using it.

Mixing variable names like --main-color instead of --text-size.

Define the variable with its name starting with double dashes, then use it with var() where needed.

5fill in blank

hard

Fill all three blanks to define a CSS variable --padding inside :root, override it inside .container, and use it in the div selector.

CSS

:root {
  [1]: 1rem;
}
.container {
  [2]: 2rem;
}
div {
  padding: [3];
}

Drag options to blanks, or click blank then click option'

A--padding

Bvar(--padding)

Dpadding

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in different places.

Using var() when defining or overriding variables.

Using property names like padding instead of variable names when defining.

Define the variable with --padding in :root, override it with the same name in .container, and use it with var(--padding) in div.

Practice

1. Where are CSS variables defined to be accessible throughout the entire webpage?

easy

A. Inside any class selector

B. Inside the :root selector

C. Inside an ID selector

D. Inside a media query only

Solution

1. Step 1: Understand global scope in CSS variables

   CSS variables defined inside :root are global and accessible anywhere.

2. Step 2: Compare with local scopes

   Variables inside class or ID selectors are local and not accessible globally.

3. Final Answer:

   Inside the :root selector -> Option B

4. Quick Check:

   Global CSS variables = :root [OK]

Hint: Global CSS variables live in :root [OK]

Common Mistakes:

• Thinking variables in classes are global
• Confusing media queries with variable scope
• Assuming ID selectors define global variables

2. Which of the following is the correct syntax to declare a CSS variable named --main-color with value blue inside a class .header?

easy

A. .header { main-color: blue; }

B. .header { var(--main-color): blue; }

C. .header { --main-color = blue; }

D. .header { --main-color: blue; }

Solution

1. Step 1: Recall CSS variable declaration syntax

   CSS variables start with two dashes and use colon to assign value, e.g., --var-name: value;.

2. Step 2: Check each option

   .header { --main-color: blue; } uses correct syntax. .header { var(--main-color): blue; } incorrectly uses var() on left side. .header { --main-color = blue; } uses equals sign which is invalid. .header { main-color: blue; } misses dashes.

3. Final Answer:

   .header { --main-color: blue; } -> Option D

4. Quick Check:

   Variable declaration = --name: value; [OK]

Hint: Declare variables with --name: value; inside selectors [OK]

Common Mistakes:

• Using equals sign instead of colon
• Using var() on left side of declaration
• Omitting the double dashes

3. Given the CSS below, what color will the text inside <div class='box'> be?

:root { --text-color: black; } .box { --text-color: red; color: var(--text-color); }

medium

A. Red

B. Default browser color

C. Black

D. Blue

Solution

1. Step 1: Identify variable scopes

   --text-color is globally black in :root, but locally red inside .box.

2. Step 2: Determine which variable applies

   Inside .box, local variable overrides global, so color: var(--text-color) uses red.

3. Final Answer:

   Red -> Option A

4. Quick Check:

   Local variable overrides global = red [OK]

Hint: Local CSS variables override global ones inside their scope [OK]

Common Mistakes:

• Assuming global variable always applies
• Confusing variable name with property name
• Ignoring local variable overrides

4. What is wrong with this CSS code if the variable --bg-color is not applying inside .card?

:root { --bg-color: yellow; } .card { background-color: var(--bg-color); } .card .content { --bg-color: green; }

medium

A. The variable --bg-color inside .content does not affect .card

B. Variables cannot be used inside background-color

C. The variable name is invalid without camelCase

D. The :root selector cannot define variables

Solution

1. Step 1: Understand variable scope in nested selectors

   Variables defined inside .card .content are local to that selector only.

2. Step 2: Check where background-color is applied

   background-color is set on .card, which uses the global variable from :root.

3. Final Answer:

   The variable --bg-color inside .content does not affect .card -> Option A

4. Quick Check:

   Local variables only affect their own scope [OK]

Hint: Local variables don't affect parent selectors [OK]

Common Mistakes:

• Thinking nested variables override parents
• Believing variables can't be used in properties
• Misunderstanding variable naming rules

5. You want a CSS variable --button-color to be blue globally but red only inside .alert buttons. Which CSS setup achieves this correctly?

hard

A. :root { --button-color: red; } button { color: var(--button-color); } .alert button { color: red; }

B. .alert button { --button-color: blue; } :root { --button-color: red; } button { color: var(--button-color); }

C. :root { --button-color: blue; } .alert button { --button-color: red; } button { color: var(--button-color); }

D. button { --button-color: blue; } .alert button { --button-color: red; color: var(--button-color); }

Solution

1. Step 1: Define global variable in :root

   Setting --button-color: blue in :root makes it global.

2. Step 2: Override variable locally inside .alert button

   Setting --button-color: red inside .alert button overrides global only there.

3. Step 3: Use variable in button color property

   Using color: var(--button-color) in button applies correct color depending on scope.

4. Final Answer:

   :root { --button-color: blue; } .alert button { --button-color: red; } button { color: var(--button-color); } -> Option C

5. Quick Check:

   Global in :root, local override in selector [OK]

Hint: Set global in :root, override locally in selector [OK]

Common Mistakes:

• Reversing global and local variable values
• Not using variable in property for local override
• Defining variables only inside buttons without global