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Declaring variables in CSS - Interactive Code Practice

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Practice - 5 Tasks
Answer the questions below
1fill in blank
easy

Complete the code to declare a CSS variable for the main color.

CSS
:root { --main-color: [1]; }
Drag options to blanks, or click blank then click option'
Ablue
B#3498db
Cred
Dgreen
Attempts:
3 left
💡 Hint
Common Mistakes
Using a color name when a hex code is expected.
Forgetting the two dashes before the variable name.
2fill in blank
medium

Complete the code to use the CSS variable for background color.

CSS
body { background-color: [1](--main-color); }
Drag options to blanks, or click blank then click option'
Aget
Buse
Cvar
Dcolor
Attempts:
3 left
💡 Hint
Common Mistakes
Using the variable name without var().
Using incorrect function names like use() or get().
3fill in blank
hard

Fix the error in the CSS variable declaration.

CSS
:root { [1]main-color: #ff6347; }
Drag options to blanks, or click blank then click option'
Avar
B-
C_
D--
Attempts:
3 left
💡 Hint
Common Mistakes
Using only one dash or underscore instead of two dashes.
Trying to use var in the declaration.
4fill in blank
hard

Fill both blanks to declare and use a CSS variable for font size.

CSS
:root { [1]font-size: 1.2rem; } p { font-size: [2](--font-size); }
Drag options to blanks, or click blank then click option'
A--
Bvar
Cfont
Dsize
Attempts:
3 left
💡 Hint
Common Mistakes
Missing dashes in declaration.
Not using var() when applying the variable.
5fill in blank
hard

Fill all three blanks to declare and use CSS variables for color and padding.

CSS
:root { [1]primary-color: #2ecc71; [2]padding: 1rem; } div { color: [3](--primary-color); padding: var(--padding); }
Drag options to blanks, or click blank then click option'
A--
Bvar
Dpadding
Attempts:
3 left
💡 Hint
Common Mistakes
Forgetting dashes in variable names.
Using variable names without var() when applying.

Practice

(1/5)
1. What is the main purpose of declaring CSS variables inside :root?
easy
A. To limit variables only to the :root selector
B. To create variables that only work in inline styles
C. To make variables available globally throughout the CSS
D. To declare variables that only apply to JavaScript

Solution

  1. Step 1: Understand the role of :root in CSS

    The :root selector targets the highest-level element in the document, usually the <html> element.

  2. Step 2: Recognize variable scope

    Declaring variables inside :root makes them global, so they can be used anywhere in the CSS.

  3. Final Answer:

    To make variables available globally throughout the CSS -> Option C

  4. Quick Check:

    Global variables = :root declaration [OK]
Hint: Declare variables in :root for global access [OK]
Common Mistakes:
  • Thinking variables declared in :root are local
  • Confusing CSS variables with JavaScript variables
  • Assuming variables only work inline
2. Which of the following is the correct syntax to declare a CSS variable named --main-color with the value #3498db inside :root?
easy
A. :root { --main-color: #3498db; }
B. :root { main-color = #3498db; }
C. :root { $main-color: #3498db; }
D. :root { var(--main-color): #3498db; }

Solution

  1. Step 1: Recall CSS variable declaration syntax

    CSS variables start with two dashes -- and are declared with a colon : inside a selector block.

  2. Step 2: Check each option

    :root { --main-color: #3498db; } uses correct syntax: --main-color: #3498db;. Others use invalid symbols or keywords.

  3. Final Answer:

    :root { --main-color: #3498db; } -> Option A

  4. Quick Check:

    Correct syntax = --name: value; [OK]
Hint: Use --name: value; inside :root [OK]
Common Mistakes:
  • Using = instead of : to assign values
  • Missing the double dash -- prefix
  • Trying to use var() in declaration
3. Given the CSS below, what color will the paragraph text be?
:root {
  --text-color: #ff0000;
}
p {
  color: var(--text-color);
}
medium
A. Red
B. Black
C. Blue
D. Green

Solution

  1. Step 1: Identify the variable value

    The variable --text-color is set to #ff0000, which is red.

  2. Step 2: Check how the variable is used

    The paragraph uses color: var(--text-color);, so it will use the red color.

  3. Final Answer:

    Red -> Option A

  4. Quick Check:

    Variable value applied = red [OK]
Hint: Match variable value with var(--name) usage [OK]
Common Mistakes:
  • Confusing hex codes with color names
  • Forgetting to use var() to apply variables
  • Assuming default color if variable is declared
4. What is wrong with this CSS code?
:root {
  --bg-color #ffffff;
}
body {
  background-color: var(--bg-color);
}
medium
A. Background color property is misspelled
B. Using var() incorrectly to apply variable
C. Variable name missing double dashes '--' prefix
D. Missing colon ':' after variable name in declaration

Solution

  1. Step 1: Check variable declaration syntax

    The declaration --bg-color #ffffff; is missing a colon : between the variable name and value.

  2. Step 2: Verify usage of variable

    The usage background-color: var(--bg-color); is correct, so the error is only in declaration.

  3. Final Answer:

    Missing colon ':' after variable name in declaration -> Option D

  4. Quick Check:

    Declaration syntax requires ':' [OK]
Hint: Always put ':' between variable name and value [OK]
Common Mistakes:
  • Forgetting colon ':' in variable declaration
  • Using var() without parentheses
  • Misspelling property names
5. You want to create a theme with two colors: --primary-color and --secondary-color. You want --secondary-color to be 50% transparent version of --primary-color. Which CSS variable declaration correctly achieves this?
hard
A. :root { --primary-color: 0, 0, 255; --secondary-color: rgba(var(--primary-color), 0.5); }
B. :root { --primary-color: #0000ff; --secondary-color: #0000ff80; }
C. :root { --primary-color: #0000ff; --secondary-color: rgba(var(--primary-color), 0.5); }
D. :root { --primary-color: #0000ff; --secondary-color: var(--primary-color, 0.5); }

Solution

  1. Step 1: Understand CSS variable limitations

    CSS variables hold values as strings; you cannot directly use var(--primary-color) inside rgba() expecting it to split into RGB components.

  2. Step 2: Check each option

    :root { --primary-color: #0000ff; --secondary-color: rgba(var(--primary-color), 0.5); } tries to use rgba(var(--primary-color), 0.5) but --primary-color is a hex string, so this won't work.
    :root { --primary-color: 0, 0, 255; --secondary-color: rgba(var(--primary-color), 0.5); } declares --primary-color as RGB components but CSS variables cannot hold multiple values like that easily.
    :root { --primary-color: #0000ff; --secondary-color: #0000ff80; } uses a hex color with alpha channel #0000ff80 which is blue with 50% opacity, correctly representing a transparent version.
    :root { --primary-color: #0000ff; --secondary-color: var(--primary-color, 0.5); } misuses var() with a second parameter that is not opacity.

  3. Final Answer:

    :root { --primary-color: #0000ff; --secondary-color: #0000ff80; } -> Option B

  4. Quick Check:

    Use hex with alpha for transparency in variables [OK]
Hint: Use hex with alpha channel for transparent colors [OK]
Common Mistakes:
  • Trying to use var() inside rgba() with hex colors
  • Declaring RGB as comma-separated string in variable
  • Misusing var() fallback parameter as opacity