🎯Part 6: 30 Bootstrap Interview Questions & Answers (Freshers to Experienced)

Whether you’re just starting out or have years of frontend experience, knowing Bootstrap is essential. It’s used in almost every real-world web project to build responsive, mobile-first, and professional websites fast.

In this article, let’s cover the top 30 most asked Bootstrap questions, including a few surprising ones that even experienced devs get wrong.

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1. ❓ What is Bootstrap?

Answer:
Bootstrap is a popular front-end toolkit that helps you design modern, responsive websites quickly using pre-built CSS, JavaScript, and HTML components.

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2. ❓ Is Bootstrap a framework or a library?

Answer:
Bootstrap is a CSS framework, not just a library.

Why a framework?

• It provides a structure (grid system, UI components, utility classes).

• It enforces a design system.

• It follows the "convention over configuration" principle.

So, it’s more than a helper — it defines how you should build.

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3. ❓ What are the key features of Bootstrap?

Answer:

• Mobile-first design

• 12-column grid system

• Pre-built components (buttons, modals, forms)

• Utility-first classes

• JavaScript plugins (Dropdowns, Carousels, etc.)

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4. ❓ Which languages is Bootstrap built with?

Answer:

• HTML (structure)

• CSS (SCSS) (styling)

• JavaScript (interactive components like modals, tooltips)

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5. ❓ What is the latest version of Bootstrap and what’s new in it?

Answer:
As of 2025, the latest version is Bootstrap 5.

What's new:

• Dropped jQuery dependency

• New utility API

• RTL support

• Improved grid and custom breakpoints

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6. ❓ How do you include Bootstrap in a project?

Answer:
You can include it in 2 ways:

1. CDN (Content Delivery Network) – for quick testing

2. Download and host locally – for production use

<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.3/dist/css/bootstrap.min.css" rel="stylesheet">

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7. ❓ What is the Bootstrap grid system?

Answer:
It’s a 12-column responsive layout system. You can divide a row into up to 12 parts using classes like .col-6, .col-md-4, etc.

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8. ❓ What are breakpoints in Bootstrap?

Answer:
Breakpoints define screen widths where layout should adjust. Bootstrap breakpoints:

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9. ❓ How do responsive columns work in Bootstrap?

Answer:
Columns adjust based on screen size using classes like:

<div class="col-12 col-md-6 col-lg-4"></div>

This creates 1 column on mobile, 2 on tablet, and 3 on desktop.

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10. ❓ What is the difference between .container, .container-fluid, and .container-{breakpoint}?

Answer:

• .container: fixed width with responsive breakpoints.

• .container-fluid: full width across all screens.

• .container-md: full width until md, then fixed width.

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11. ❓ What are utility classes in Bootstrap?

Answer:
Utility classes are small, reusable classes for margin, padding, text, colors, etc.

Examples:

.mt-3, .text-center, .bg-primary

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12. ❓ How is spacing handled in Bootstrap?

Answer:
Bootstrap uses margin/padding utilities like:

.mt-3  => margin-top: 1rem;
.px-2  => padding-left and right: 0.5rem;

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13. ❓ What are some important Bootstrap components?

Answer:

• Buttons

• Cards

• Alerts

• Modals

• Navbar

• Accordions

• Carousel

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14. ❓ How do you create a button in Bootstrap?

Answer:

<button class="btn btn-primary">Click me</button>

Available button types: btn-primary, btn-success, btn-danger, etc.

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15. ❓ What is a modal in Bootstrap?

Answer:
A modal is a dialog box/popup used for alerts, forms, etc.

Example:

<button data-bs-toggle="modal" data-bs-target="#exampleModal">Open Modal</button>

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16. ❓ What is a Bootstrap card?

Answer:
Card is a flexible container with options like headers, images, footers.

<div class="card">
  <img src="..." class="card-img-top">
  <div class="card-body">...</div>
</div>

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17. ❓ How is navbar implemented in Bootstrap?

Answer:

<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <a class="navbar-brand" href="#">Logo</a>
</nav>

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18. ❓ How do you create a responsive image in Bootstrap?

Answer:
Use .img-fluid:

<img src="img.jpg" class="img-fluid" alt="Responsive image">

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19. ❓ How does Bootstrap support dark mode?

Answer:
You can use dark variants like bg-dark, navbar-dark, and custom themes. Bootstrap 5 also supports dark mode toggle via custom CSS and utility classes.

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20. ❓ What is flexbox in Bootstrap?

Answer:
Bootstrap uses Flexbox to create layouts. Use .d-flex, .justify-content-between, etc.

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21. ❓ How do you vertically center an element using Bootstrap?

Answer:

<div class="d-flex align-items-center" style="height: 100vh;">
  <div class="mx-auto">Centered</div>
</div>

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22. ❓ What is the difference between d-none and invisible?

Answer:

• d-none: removes the element from layout and hides it.

• invisible: keeps the space but makes it invisible.

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23. ❓ What are Bootstrap badges?

Answer:
Badges are used for notifications:

<span class="badge bg-success">New</span>

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24. ❓ How do you customize Bootstrap?

Answer:

• Override styles using custom CSS

• Use SASS variables

• Use Bootstrap’s utility API

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25. ❓ What is Bootstrap Reboot?

Answer:
Bootstrap Reboot is a CSS reset that normalizes styles across browsers. It’s included by default.

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26. ❓ How is Bootstrap 5 different from Bootstrap 4?

Answer:

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27. ❓ What is order in Bootstrap Flexbox?

Answer:
It controls the order of flex items.

<div class="order-2">Second</div>
<div class="order-1">First</div>

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28. ❓ How do you align text using Bootstrap?

Answer:
Use .text-start, .text-center, .text-end.

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29. ❓ Can Bootstrap be used with React or Angular?

Answer:
Yes, Bootstrap works with React/Angular. For React, use React-Bootstrap or Bootstrap with plain HTML classes.

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30. ❓ What are best practices when using Bootstrap?

Answer:

• Don’t override too many default styles.

• Use utility classes instead of writing custom CSS.

• Use responsive breakpoints properly.

• Keep layout semantic and accessible.

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🔚 Conclusion:

Bootstrap makes development faster, cleaner, and more responsive — that’s why companies expect frontend developers to master it. Understanding these 30 questions will prepare you for real-world interviews, whether you're applying for a startup or a big tech firm.

✅ Next Up: Want Part 7 with JavaScript DOM-based questions or continue deeper with Bootstrap + SASS or JavaScript frameworks?

If you have any query , please freely write your query in comment section .