Mixing column widths in Bootsrap - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Bootstrap column width behavior

In Bootstrap's grid system, what happens if you mix fixed-width columns (like col-3) with auto-width columns (like col) inside the same row?

A Auto-width columns shrink to zero width and are not visible.

B All columns become fixed width based on the largest fixed-width column.

C The fixed-width columns keep their size, and the auto-width columns share the remaining space equally.

D The row breaks into multiple lines to fit all columns.

💡 Hint

Think about how Bootstrap distributes space when some columns have fixed sizes and others don't.

Bootstrap's grid allows mixing fixed-width columns (like col-3) with flexible columns (col). The fixed-width columns take their specified width, and the remaining space is divided equally among the flexible columns.

📝 Syntax

intermediate

Correct Bootstrap column class usage

Which option correctly creates a row with three columns where the first column is 4 units wide, the second column auto-adjusts, and the third column is 3 units wide?

Bootsrap

<div class="row">
  <!-- columns here -->
</div>

A <div class="col-3"></div><div class="col-4"></div><div class="col"></div>

B <div class="col-4"></div><div class="col"></div><div class="col-3"></div>

C <div class="col"></div><div class="col-4"></div><div class="col-3"></div>

D <div class="col-4"></div><div class="col-3"></div><div class="col"></div>

💡 Hint

Remember the order: first column 4 units, second auto, third 3 units.

The correct order is col-4, then col for auto width, then col-3. This matches the requirement exactly.

❓ rendering

advanced

Visual output of mixed column widths

What will you see in the browser when you use this Bootstrap code inside a container?

<div class="row">
  <div class="col-2 bg-primary text-white">A</div>
  <div class="col bg-success text-white">B</div>
  <div class="col-3 bg-danger text-white">C</div>
</div>

A A narrow blue box labeled 'A', a green box labeled 'B' filling leftover space, and a wider red box labeled 'C'.

B Three equal boxes labeled A, B, and C with equal widths and colors blue, green, and red.

C Boxes A and C stacked vertically with B filling the full width below them.

D Only boxes A and C appear side by side; box B is hidden.

💡 Hint

Look at the column classes and their widths.

The col-2 and col-3 columns have fixed widths. The col column fills the leftover space. Colors and labels help identify each box visually.

❓ selector

advanced

CSS selector for mixed Bootstrap columns

You want to style only the auto-width columns inside a Bootstrap row that also has fixed-width columns. Which CSS selector targets only the auto-width columns (with class col) inside a .row?

A .row > div:not(.col)

B .row > .col:not([class*='col-'])

C .row > [class^='col-']

D .row > .col

💡 Hint

Remember that auto-width columns have the class exactly 'col'.

The class col alone identifies auto-width columns. So .row > .col selects them directly. Option D tries to exclude fixed-width columns but is unnecessary because fixed-width columns do not have the col class; they use col-{n} classes like col-3.

❓ accessibility

expert

Ensuring accessibility with mixed column widths

You have a Bootstrap row with mixed column widths. What is the best practice to ensure screen readers understand the layout and content order correctly?

A Use semantic HTML elements inside columns and ensure logical DOM order matches visual order.

B Add <code>aria-hidden="true"</code> to fixed-width columns to skip them.

C Use <code>tabindex="-1"</code> on auto-width columns to prevent keyboard focus.

D Wrap all columns in a single <code>div</code> with <code>role="presentation"</code>.

💡 Hint

Think about how screen readers read content and the importance of semantic structure.

Using semantic HTML and keeping the DOM order logical ensures screen readers read content in the correct sequence. Hiding or removing focus from columns can confuse users. Role presentation removes meaning and should not be used for content containers.

Practice

1. What does the class col-6 mean in Bootstrap's grid system?

easy

A. The column is hidden on screens smaller than 6 inches.

B. The column takes up 6 pixels width.

C. The column takes up half the row width (6 out of 12 parts).

D. The column is fixed to 6 rem units wide.

Solution

1. Step 1: Understand Bootstrap grid basics

   Bootstrap divides a row into 12 equal parts for layout.

2. Step 2: Interpret col-6 meaning

   The class col-6 means the column uses 6 of those 12 parts, which is half the row width.

3. Final Answer:

   The column takes up half the row width (6 out of 12 parts). -> Option C

4. Quick Check:

   12 parts total, 6 parts used = half width [OK]

Hint: Remember: col-6 means 6/12 width, or half the row [OK]

Common Mistakes:

• Thinking col-6 means 6 pixels wide
• Confusing col-6 with fixed width units
• Assuming col-6 hides the column

2. Which of the following is the correct way to make a column take 4 parts on medium screens and 12 parts on small screens?

easy

A. <div class='col-12 col-md-4'></div>

B. <div class='col-lg-4 col-12'></div>

C. <div class='col-4 col-md-12'></div>

D. <div class='col-md-12 col-4'></div>

Solution

1. Step 1: Understand responsive classes order

   Bootstrap applies classes from smallest to largest screen sizes. The class without breakpoint applies to all sizes unless overridden.

2. Step 2: Choose correct class order

   To have 12 parts on small screens and 4 parts on medium and up, use col-12 for small and col-md-4 for medium screens.

3. Final Answer:

   <div class='col-12 col-md-4'></div> -> Option A

4. Quick Check:

   Small = col-12, Medium = col-md-4 [OK]

Hint: Put smaller screen class first, then medium with breakpoint [OK]

Common Mistakes:

• Reversing the order of classes
• Using wrong breakpoint prefixes
• Assuming col-4 applies to small screens

3. Given this HTML snippet:

<div class='row'>
  <div class='col-3'>A</div>
  <div class='col-6'>B</div>
  <div class='col-3'>C</div>
</div>

How will the columns appear on a large screen?

medium

A. Three columns stacked vertically, each full width

B. Three columns: A (25%), B (50%), C (25%) width in one row

C. Two columns: A and B share one row, C on next row

D. Columns A and C are hidden, only B shows

Solution

1. Step 1: Add column widths

   Columns have classes col-3, col-6, and col-3, which add up to 3+6+3=12 parts.

2. Step 2: Understand layout on large screens

   Since total is 12, all columns fit in one row side by side with widths 25%, 50%, and 25% respectively.

3. Final Answer:

   Three columns: A (25%), B (50%), C (25%) width in one row -> Option B

4. Quick Check:

   3+6+3=12 parts, fits in one row [OK]

Hint: Sum col-* numbers; if 12, columns share one row [OK]

Common Mistakes:

• Thinking columns stack vertically by default
• Assuming columns overflow to next row
• Confusing col-3 with 3 pixels

4. Identify the error in this Bootstrap code:

<div class='row'>
  <div class='col-5'>X</div>
  <div class='col-8'>Y</div>
</div>

medium

A. The total column width exceeds 12, causing layout issues.

B. The class names should be col-6 and col-6 instead.

C. The row class is missing a container wrapper.

D. The columns need to use col-md-* classes instead.

Solution

1. Step 1: Calculate total column width

   Adding col-5 and col-8 gives 5 + 8 = 13, which is more than 12.

2. Step 2: Understand Bootstrap grid limits

   Bootstrap rows can only hold 12 parts per row. Exceeding 12 causes the second column to wrap or break layout.

3. Final Answer:

   The total column width exceeds 12, causing layout issues. -> Option A

4. Quick Check:

   5 + 8 = 13 > 12 breaks grid [OK]

Hint: Sum col-* numbers; must not exceed 12 per row [OK]

Common Mistakes:

• Ignoring total width exceeding 12
• Thinking col-5 and col-8 fit in one row
• Assuming container is mandatory for row

5. You want a layout with three columns on large screens: left column 3 parts, middle column 6 parts, right column 3 parts. On small screens, all columns should stack full width. Which Bootstrap classes achieve this?

hard

A. <div class='col-3 col-lg-12'> for left and right, <div class='col-6 col-lg-12'> for middle

B. <div class='col-xl-3 col-12'> for left and right, <div class='col-xl-6 col-12'> for middle

C. <div class='col-lg-12 col-3'> for left and right, <div class='col-lg-12 col-6'> for middle

D. <div class='col-12 col-lg-3'> for left and right, <div class='col-12 col-lg-6'> for middle

Solution

1. Step 1: Define small screen behavior

   On small screens, columns stack full width, so use col-12 for all columns.

2. Step 2: Define large screen behavior

   On large screens, left and right columns take 3 parts (col-lg-3), middle takes 6 parts (col-lg-6).

3. Step 3: Combine classes correctly

   Use col-12 col-lg-3 for left and right, and col-12 col-lg-6 for middle to apply small screen first, then large screen overrides.

4. Final Answer:

   <div class='col-12 col-lg-3'> for left and right, <div class='col-12 col-lg-6'> for middle -> Option D

5. Quick Check:

   Small = col-12, Large = col-lg-3 or col-lg-6 [OK]

Hint: Write small screen class first, then large screen class [OK]

Common Mistakes:

• Reversing class order causing wrong widths
• Using col-3 for small screens instead of col-12
• Mixing breakpoint prefixes incorrectly