Lesson 5: Understanding Breakpoints & Flexbox in Bootstrap

📌 Objective: Learn how breakpoints work in Bootstrap and how to use Flexbox utilities for responsive layouts.

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🔹 1. What Are Bootstrap Breakpoints?

Breakpoints are specific screen widths where Bootstrap adjusts layouts based on device size.
This makes Bootstrap mobile-first, meaning designs start with small screens and scale up.

💡 Why Use Breakpoints?
✔️ Ensure content fits different screen sizes
✔️ Design mobile-first, then scale for larger devices
✔️ Create custom layouts for specific screen widths

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🔹 2. Bootstrap’s Responsive Breakpoints

Breakpoint	Class Prefix	Screen Size
Extra Small	.col-	<576px
Small	.col-sm-	≥576px
Medium	.col-md-	≥768px
Large	.col-lg-	≥992px
Extra Large	.col-xl-	≥1200px
XXL	.col-xxl-	≥1400px

💡 How to Use Breakpoints?

• Add prefixes (.col-sm-*, .col-md-*, etc.) to specify layouts for different screen sizes.

✅ Example: Responsive Columns

🔹 What happens?

• On small screens (sm) → Each column takes full width (12/12)
• On medium screens (md) → Columns take half width (6/12)
• On large screens (lg) → First column takes 4/12, second takes 8/12

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🔹 3. Introduction to Bootstrap Flexbox

💡 What is Flexbox?
Flexbox is a CSS layout model that makes it easier to align elements horizontally or vertically.

💡 Why Use Flexbox in Bootstrap?
✔️ Easier alignment of content
✔️ Equal column heights automatically
✔️ Works with Bootstrap’s grid system

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🔹 4. Bootstrap Flexbox Utilities

1️⃣ Display Flex (d-flex)

• Enables flexbox layout on an element.

✅ Example: Applying d-flex to a Row

🔹 What happens? The elements align horizontally in a row.

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2️⃣ Justify Content (justify-content-*)

Controls horizontal alignment inside a flex container.

Class	Alignment
.justify-content-start	Left-aligned
.justify-content-center	Centered
.justify-content-end	Right-aligned
.justify-content-between	Evenly distributed
.justify-content-around	Equal space around

✅ Example: Centering Content Horizontally

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3️⃣ Align Items (align-items-*)

Controls vertical alignment of flex items.

Class	Alignment
.align-items-start	Align to top
.align-items-center	Align to center
.align-items-end	Align to bottom

✅ Example: Centering Content Vertically

🔹 What happens? The box is centered vertically inside the div.

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4️⃣ Flex Direction (flex-*)

Controls the direction of flex items.

Class	Effect
.flex-row	Default (left to right)
.flex-row-reverse	Right to left
.flex-column	Stacked vertically
.flex-column-reverse	Stacked bottom to top

✅ Example: Stacking Items Vertically

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🔹 5. Combining Breakpoints & Flexbox

You can use breakpoints to adjust Flexbox behavior at different screen sizes.

✅ Example: Changing Alignment Based on Screen Size

🔹 What happens?

• On small screens → Items stack vertically (flex-column)
• On medium screens (md) & larger → Items align horizontally (flex-row)

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📝 Lesson Recap Quiz

🎯 Test your understanding of breakpoints & Flexbox.

📌 Multiple-Choice Questions (MCQs)

1️⃣ What is the default number of columns in Bootstrap’s grid system?
a) 6
b) 8
c) 12
d) 16

✅ Correct Answer: c) 12

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2️⃣ Which Bootstrap class makes an element a Flexbox container?
a) .display-flex
b) .flexbox
c) .d-flex
d) .row-flex

✅ Correct Answer: c) .d-flex

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3️⃣ What does .justify-content-between do?
a) Centers items inside a Flexbox container
b) Aligns items to the start of the row
c) Distributes items with space between them
d) Makes items stack vertically

✅ Correct Answer: c) Distributes items with space between them

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📌 True or False

4️⃣ Bootstrap’s grid system is based on Flexbox.
✅ Answer: True

5️⃣ The .flex-column class makes items align horizontally.
✅ Answer: False (It stacks items vertically.)

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🎯 Practical Challenge

✅ Create a responsive navigation bar using d-flex and .justify-content-between.
✅ Adjust alignment for different screen sizes using breakpoints (.flex-column, .flex-row).
✅ Post your solution in the discussion forum for feedback!

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🎓 Lesson Summary

✅ Breakpoints define responsive behavior at different screen sizes.
✅ .col-sm-*, .col-md-*, .col-lg-* adjust column widths at different breakpoints.
✅ Flexbox (d-flex) simplifies alignment, spacing, and responsiveness.
✅ Use justify-content-*, align-items-*, and flex-column/row for dynamic layouts.