Nth-child selector in CSS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the :nth-child() selector do in CSS?

It selects elements based on their position among siblings in the parent element. For example, :nth-child(2) selects the second child element.

beginner

How would you select every even child element using :nth-child()?

Use :nth-child(even). This selects the 2nd, 4th, 6th, and so on children.

intermediate

What does :nth-child(3n+1) select?

It selects every 3rd element starting from the first child. So, 1st, 4th, 7th, 10th, etc.

beginner

True or False: :nth-child() counts only elements of a specific type.

False. :nth-child() counts all child elements regardless of type. To select specific types, use :nth-of-type().

beginner

How can :nth-child() help in creating striped table rows?

By selecting even or odd rows with tr:nth-child(even) or tr:nth-child(odd), you can style alternating rows differently for better readability.

Which CSS selector targets every 3rd child starting from the second child?

A :nth-child(3n-2)

B :nth-child(2n+3)

C :nth-child(2n+1)

D :nth-child(3n+2)

The formula 3n+2 selects children at positions 2, 5, 8, etc.

What does :nth-child(odd) select?

A All children at odd positions (1st, 3rd, 5th...)

B All children at even positions

C Only the first child

D Only the last child

odd matches 1, 3, 5, and so on.

If you want to style only the 4th child element, which selector do you use?

A :nth-child(even)

B :nth-child(3n)

C :nth-child(4)

D :nth-child(odd)

:nth-child(4) targets exactly the 4th child.

Does :nth-child() consider element types when counting children?

A Yes, it counts only elements of the same type

B No, it counts all child elements regardless of type

C It counts only text nodes

D It counts only elements with a class

:nth-child() counts all child elements, not filtered by type.

Which selector would you use to color every even row in a table?

A tr:nth-child(even)

B tr:nth-child(odd)

C tr:nth-of-type(odd)

D tr:nth-of-type(even)

tr:nth-child(even) selects even rows for styling.

Explain how the :nth-child() selector works and give an example of using a formula inside it.

Think about how you count items in a list and how formulas can pick certain positions.

Describe the difference between :nth-child() and :nth-of-type() selectors.

Consider if you want to select all children or only specific tags.

Practice

1. What does the CSS selector li:nth-child(3) select?

easy

A. The third <li> element inside its parent

B. Every third <li> element in the whole document

C. The third child of any type inside the parent

D. All <li> elements except the third one

Solution

1. Step 1: Understand nth-child selector

   The nth-child(n) selector targets the element that is the nth child of its parent, counting all types of children.

2. Step 2: Apply to li:nth-child(3)

   This means it selects the li element only if it is the third child of its parent. It does not select the third li if other elements come before it.

3. Final Answer:

   The third child of any type inside the parent -> Option C

4. Quick Check:

   li:nth-child(3) = third child of any type [OK]

Hint: Selects element if it is nth child of parent, not nth of type [OK]

Common Mistakes:

• Thinking it selects the nth element of that type globally
• Confusing nth-child with nth-of-type selector
• Assuming it selects every nth element regardless of type

2. Which of the following is the correct syntax to select every even div inside a container using :nth-child?

easy

A. div:nth-child(2n+1)

B. div:nth-child(even)

C. div:nth-child(odd)

D. div:nth-child(2n-1)

Solution

1. Step 1: Recall even keyword meaning

   The keyword even in :nth-child(even) selects all even-numbered children (2nd, 4th, 6th, etc.).

2. Step 2: Match syntax to select even div elements

   Using div:nth-child(even) selects every div that is an even child of its parent.

3. Final Answer:

   div:nth-child(even) -> Option B

4. Quick Check:

   even = every 2nd child [OK]

Hint: Use 'even' keyword to select every 2nd child easily [OK]

Common Mistakes:

• Using odd instead of even
• Using formulas like 2n+1 which select odd children
• Confusing nth-child with nth-of-type

3. Given this HTML:

<ul>
  <li>One</li>
  <li>Two</li>
  <li>Three</li>
  <li>Four</li>
  <li>Five</li>
</ul>

And CSS:

li:nth-child(2n) { color: red; }

Which list items will appear red in the browser?

medium

A. Only Two

B. One, Three, and Five

C. All list items

D. Two and Four

Solution

1. Step 1: Understand 2n in nth-child

   The formula 2n selects every even child: 2nd, 4th, 6th, etc.

2. Step 2: Apply to the list items

   Items 2 (Two) and 4 (Four) are even children, so they get the red color.

3. Final Answer:

   Two and Four -> Option D

4. Quick Check:

   2n = even children = Two, Four [OK]

Hint: 2n selects even children: 2,4,6... [OK]

Common Mistakes:

• Thinking 2n selects odd children
• Confusing nth-child with nth-of-type
• Assuming all items get styled

4. What is wrong with this CSS if the goal is to color every 3rd p element blue?

p:nth-child(3n+1) {
  color: blue;
}

medium

A. It colors the 1st, 4th, 7th p, not every 3rd

B. Syntax error in the formula

C. It colors only the 3rd p element

D. It colors all p elements

Solution

1. Step 1: Analyze the formula 3n+1

   The formula 3n+1 selects children at positions 1, 4, 7, 10, ...

2. Step 2: Compare with the goal of every 3rd element

   Every 3rd element means positions 3, 6, 9, ... which is 3n, not 3n+1.

3. Final Answer:

   It colors the 1st, 4th, 7th <p>, not every 3rd -> Option A

4. Quick Check:

   3n+1 = 1,4,7... not every 3rd [OK]

Hint: Use 3n for every 3rd, not 3n+1 [OK]

Common Mistakes:

• Using 3n+1 instead of 3n for every 3rd child
• Confusing formula offsets
• Expecting 3n+1 to select 3rd, 6th, 9th

5. You want to style only the 2nd and 4th li elements inside a ul without styling the 6th or others. Which CSS selector achieves this?

hard

A. li:nth-child(2), li:nth-child(4)

B. li:nth-child(2n)

C. li:nth-child(2n+2)

D. li:nth-child(2n):not(:nth-child(6))

Solution

1. Step 1: Understand the goal

   We want to style only the 2nd and 4th li elements, excluding the 6th or any others.

2. Step 2: Evaluate each option

   li:nth-child(2n):not(:nth-child(6)) selects every even li except the 6th, but also includes 8th, 10th, etc. li:nth-child(2n) selects all even li elements (2nd, 4th, 6th, ...). li:nth-child(2n+2) selects 2nd, 4th, 6th, ... as well. li:nth-child(2), li:nth-child(4) explicitly selects only the 2nd and 4th li elements.

3. Final Answer:

   li:nth-child(2), li:nth-child(4) -> Option A

4. Quick Check:

   Explicitly list 2nd and 4th for exact selection [OK]

Hint: List exact children with commas for precise selection [OK]

Common Mistakes:

• Using formulas that select more than needed
• Trying to exclude with :not() but missing others
• Assuming 2n+2 excludes 6th child