CSS Flexbox Explained – Complete Guide to Flexible Containers and Flex Items

CSS Flexbox gives you the tools to create basic and advanced website layouts in flexible and responsive ways.

This tutorial discusses everything you need to know to use Flexbox like a pro.

Table of Contents

1. What Is Flexbox?
2. Flex Container vs. Flex Item: What's the Difference?
3. What Is a flex Value in CSS?
4. What Is an inline-flex Value in CSS?
5. Properties for Specifying Flexbox's Layout
6. What Are the Flexible Containers Properties?
7. What Is Flexbox's flex-direction Property?
8. What Is Flexbox's flex-wrap Property?
9. What Is Flexbox's flex-flow Property?
10. What Is Flexbox's justify-content Property?
11. What Is Flexbox's align-items Property?
12. What Is Flexbox's align-content Property?
13. What Are the Flexible Items Properties?
14. What Is Flexbox's align-self Property?
15. What Is Flexbox's order Property?
16. What Is Flexbox's flex-grow Property?
17. What Is Flexbox's flex-shrink Property?
18. What Is Flexbox's flex-basis Property?
19. What Is Flexbox's flex Property?
20. How to Center Elements Horizontally with Flexbox
21. How to Center Elements Vertically with Flexbox
22. How to Center Elements Horizontally and Vertically with Flexbox
23. Overview

So, without any further ado, let's understand what Flexbox is.

What Is Flexbox?

Flexbox makes browsers display selected HTML elements as flexible box models.

Flexbox allows easy resizing and repositioning of a flexible container and its items one-dimensionally.

Note:

• "One-dimensionally" means Flexbox allows laying out box models in a row or column at a time. In other words, Flexbox cannot lay out box models in a row and column at the same time.
• Flexbox is sometimes called a flexible box layout module.
• Use the grid layout module if you need to resize and reposition elements two-dimensionally.

Flex Container vs. Flex Item: What's the Difference?

A flex container is an HTML element whose display property's value is flex or inline-flex.

Flex items are the direct children of a flex container.

A flex container (the large yellow area in the image) is an HTML element whose display property's value is flex or inline-flex. Flex items (the smaller boxes within the yellow container) are the direct children of a flex container.

What Is a flex Value in CSS?

flex tells browsers to display the selected HTML element as a block-level flexible box model.

In other words, setting an element's display property's value to flex turns the box model into a block-level flexbox.

Here's an example:

section {
  display: flex;
  background-color: orange;
  margin: 10px;
  padding: 7px;
}

Try it on StackBlitz

The snippet above used the flex value to convert the HTML document's <section> elements from regular <section> nodes to block-level flexible box models.

Note:

• Converting an HTML node to a flexible box model makes the element's direct children become flexible items.
• The display: flex directive only affects a box model and its direct children. It does not affect grandchildren nodes.

Let's now discuss inline-flex.

What Is an inline-flex Value in CSS?

inline-flex tells browsers to display the selected HTML element as an inline-level flexible box model.

In other words, setting an element's display property's value to inline-flex turns the box model into an inline-level flexbox.

Here's an example:

section {
  display: inline-flex;
  background-color: orange;
  margin: 10px;
  padding: 7px;
}

Try it on StackBlitz

The snippet above used the inline-flex value to convert the HTML document's <section> elements from regular <section> nodes to inline-level flexible box models.

Note:

• Converting an HTML node to a flexible box model makes the element's direct children become flexible items.
• The display: inline-flex directive only affects a box model and its direct children. It does not affect grandchildren nodes.

Properties for Specifying Flexbox's Layout

On converting a regular HTML element to a flex (or inline-flex) box model, Flexbox provides two categories of properties for positioning the flexible box and its direct children:

• Flexible containers properties
• Flexible items properties

What Are the Flexible Containers Properties?

A flexible container's properties specify how browsers should layout items within the flexible box model.

Note: We define a flexible container's property on the flex container, not its items.

The six (6) types of flex container properties are:

• flex-direction
• flex-wrap
• flex-flow
• justify-content
• align-items
• align-content

Let's discuss the six types now.

What Is Flexbox's flex-direction Property?

flex-direction tells browsers the specific direction (row or column) they should lay out a flexible container's direct children.

In other words, flex-direction defines a flexbox's main axis.

A Flexbox's main axis is the layout orientation defined by a flex-direction property. Its cross axis is the perpendicular orientation to the main axis.

Here's an example:

section {
  display: flex;
  flex-direction: column;
  background-color: orange;
  margin: 10px;
  padding: 7px;
}

Try it on StackBlitz

The snippet above organized the flexible <section> containers' items in the column direction of your browser's default language.

Tip: Use flex-direction: column-reverse (or flex-direction: row-reverse) to reverse the browser's layout direction.

What Is Flexbox's flex-wrap Property?

flex-wrap specifies whether browsers should wrap overflown flexible items onto multiple lines.

The flex-wrap property accepts the following values:

• nowrap
• wrap
• wrap-reverse

Let's discuss the three values.

What is flex-wrap: nowrap in CSS flexbox?

nowrap is flex-wrap's default value. It forces all items within a flexible container into a single line (that is, row-wise or column-wise direction).

In other words, nowrap tells browsers not to wrap a flexible container's items.

Note: Suppose the total width (or height) of all the items in a flexible container is greater than the flexbox's width (or height). In such a case, nowrap will cause the elements to overflow out of the container.

Here's an example:

section {
  width: 130px;
  display: flex;
  flex-wrap: nowrap;
  background-color: orange;
  margin: 10px;
  padding: 7px;
}

Try it on StackBlitz

The snippet above used nowrap to force browsers to lay out the flexible containers' items in a single line.

What is flex-wrap: wrap in CSS flexbox?

wrap moves all overflow items within a flexible container to the next line.

In other words, wrap tells browsers to wrap a flexible container's overflow items.

Here's an example:

section {
  width: 130px;
  display: flex;
  flex-wrap: wrap;
  background-color: orange;
  margin: 10px;
  padding: 7px;
}

Try it on StackBlitz

We used wrap to wrap the flexible containers' overflow items to the next line.

What is flex-wrap: wrap-reverse in CSS flexbox?

wrap-reverse moves all overflow items within a flexible container to the next line in reverse order.

Note: wrap-reverse does the same thing as wrap—but in reverse order.

Here's an example:

section {
  width: 130px;
  display: flex;
  flex-wrap: wrap-reverse;
  background-color: orange;
  margin: 10px;
  padding: 7px;
}

Try it on StackBlitz

We used wrap-reverse to wrap the flexible containers' overflow items to the next line in reverse order.

What Is Flexbox's flex-flow Property?

flex-flow is a shorthand for the flex-direction and flex-wrap properties.

In other words, instead of writing:

section {
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
}

You can alternatively use the flex-flow property to shorten your code like so:

section {
  display: flex;
  flex-flow: column wrap;
}

What Is Flexbox's justify-content Property?

justify-content specifies how browsers should position a flexible container's items along the flexbox's main axis.

The justify-content property accepts the following values:

• flex-start
• center
• flex-end
• space-between
• space-around
• space-evenly

Let's discuss these six values.

What is justify-content: flex-start in CSS Flexbox?

flex-start is justify-content's default value. It aligns a flexible container's items with the main-start edge of the flexbox's main axis.

flex-start aligns a flexible container's items with the main-start side of the flexbox's main axis.

Here's an example:

section {
  display: flex;
  justify-content: flex-start;
  background-color: orange;
  margin: 10px;
}

Try it on StackBlitz

The snippet above used the flex-start value to align the flexible container's items to the flexbox's main-start edge.

What is justify-content: center in CSS Flexbox?

center aligns a flexible container's items to the center of the flexbox's main axis.

center aligns a flexible container's items to the center of the flexbox's main axis.

Here's an example:

section {
  display: flex;
  justify-content: center;
  background-color: orange;
  margin: 10px;
}

Try it on StackBlitz

We used the center value to align the flexible container's items to the center of the flexbox.

What is justify-content: flex-end in CSS Flexbox?

flex-end aligns a flexible container's items with the main-end side of the flexbox's main axis.

flex-end aligns a flexible container's items with the main-end side of the flexbox's main axis.

Here's an example:

section {
  display: flex;
  justify-content: flex-end;
  background-color: orange;
  margin: 10px;
}

Try it on StackBlitz

We used the flex-end value to align the flexible container's items to the flexbox's main-end side.

What is justify-content: space-between in CSS Flexbox?

space-between does the following:

• It aligns a flexible container's first item with the main-start edge of the flexbox's main axis.
• It aligns the container's last item with the main-end edge of the flexbox's main axis.
• It creates even spacing between each pair of items between the first and last item.

space-between creates even spacing between each pair of items between the first and last item.

Here's an example:

section {
  display: flex;
  justify-content: space-between;
  background-color: orange;
  margin: 10px;
}

Try it on StackBlitz

The snippet above used the space-between value to create even spacing between each pair of items between the first and last flex item.

What is justify-content: space-around in CSS Flexbox?

space-around assigns equal spacing to each side of a flexible container's items.

Therefore, the space before the first item and after the last element is half the width of the space between each pair of elements.

space-around assigns equal spacing to each side of a flexible container's items.

Here's an example:

section {
  display: flex;
  justify-content: space-around;
  background-color: orange;
  margin: 10px;
}

Try it on StackBlitz

The snippet above used the space-around value to assign equal spacing to each side of the flexible container's items.

What is justify-content: space-evenly in CSS Flexbox?

space-evenly assigns even spacing to both ends of a flexible container and between its items.

space-evenly assigns even spacing to both ends of a flexible container and between its items.

Here's an example:

section {
  display: flex;
  justify-content: space-evenly;
  background-color: orange;
  margin: 10px;
}

Try it on StackBlitz

We used the space-evenly value to assign even spacing to both ends of the flexbox and between its items.

Let's now discuss the fifth type of flexible container property.

What Is Flexbox's align-items Property?

align-items specifies how browsers should position a flexible container's items along the cross-axis of the flexbox.

The align-items property accepts the following values:

• stretch
• flex-start
• center
• flex-end
• baseline

Let's discuss the five values.

What is align-items: stretch in CSS Flexbox?

stretch is align-items' default value. It stretches a flexible container's items to fill the flexbox's cross-axis.

stretch stretches a flexible container's items to fill the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  align-items: stretch;
  background-color: orange;
  margin: 10px;
  height: 300px;
}

Try it on StackBlitz

The snippet above used the stretch value to stretch the flexible items to fill the <section>'s cross-axis.

What is align-items: flex-start in CSS Flexbox?

flex-start aligns a flexible container's items with the cross-start edge of the flexbox's cross-axis.

flex-start aligns a flexible container's items with the cross-start edge of the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  align-items: flex-start;
  background-color: orange;
  margin: 10px;
  height: 300px;
}

Try it on StackBlitz

We used the flex-start value to align the flexible items to the cross-start edge of the <section>'s cross-axis.

What is align-items: center in CSS Flexbox?

center aligns a flexible container's items to the center of the flexbox's cross-axis.

center aligns a flexible container's items to the center of the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  align-items: center;
  background-color: orange;
  margin: 10px;
  height: 300px;
}

Try it on StackBlitz

The snippet above used the center value to align the flexible items to the center of the <section>'s cross-axis.

What is align-items: flex-end in CSS Flexbox?

flex-end aligns a flexible container's items with the cross-end edge of the flexbox's cross-axis.

flex-end aligns a flexible container's items with the cross-end edge of the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  align-items: flex-end;
  background-color: orange;
  margin: 10px;
  height: 300px;
}

Try it on StackBlitz

We used the flex-end value to align the flexible items to the cross-end edge of the <section>'s cross-axis.

What is align-items: baseline in CSS Flexbox?

baseline aligns a flexible container's items with the baseline of the flexbox's cross-axis.

baseline aligns a flexible container's items with the baseline of the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  align-items: baseline;
  background-color: orange;
  margin: 10px;
}

Try it on StackBlitz

The snippet above used the baseline value to align the flexible items to the <section>'s baseline.

Now, let's talk about the sixth CSS flexible container property type.

What Is Flexbox's align-content Property?

align-content specifies how browsers should position a flexible container's lines along the flexbox's cross-axis.

Note: The align-content property does not affect a flexbox with only one line—for instance, a flexible container with flex-wrap: nowrap. In other words, align-content works only on flexboxes with multiple lines.

The align-content property accepts the following values:

• stretch
• flex-start
• center
• flex-end
• space-between
• space-around
• space-evenly

Let's discuss the seven values.

What is align-content: stretch in CSS Flexbox?

stretch is align-content's default value. It stretches the flexible container's lines to fill the flexbox's cross-axis.

stretch stretches the flexible container's lines to fill the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  flex-wrap: wrap;
  align-content: stretch;
  background-color: orange;
  margin: 10px;
  width: 90px;
  height: 500px;
}

Try it on StackBlitz

The snippet above used the stretch value to stretch the flexbox's lines to fill the <section>'s cross-axis.

What is align-content: flex-start in CSS Flexbox?

flex-start aligns a flexible container's lines with the cross-start edge of the flexbox's cross-axis.

flex-start aligns a flexible container's lines with the cross-start edge of the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  flex-wrap: wrap;
  align-content: flex-start;
  background-color: orange;
  margin: 10px;
  width: 90px;
  height: 500px;
}

Try it on StackBlitz

The snippet above used the flex-start value to align the flexbox's lines to the cross-start edge of the <section>'s cross-axis.

What is align-content: center in CSS Flexbox?

center aligns a flexible container's lines to the center of the flexbox's cross-axis.

center aligns a flexible container's lines to the center of the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  flex-wrap: wrap;
  align-content: center;
  background-color: orange;
  margin: 10px;
  width: 90px;
  height: 500px;
}

Try it on StackBlitz

We used the center value to align the flexbox's lines to the center of the <section>'s cross-axis.

What is align-content: flex-end in CSS Flexbox?

flex-end aligns a flexible container's lines with the cross-end edge of the flexbox's cross-axis.

flex-end aligns a flexible container's lines with the cross-end edge of the flexbox's cross-axis.

Here's an example:

section {
  display: flex;
  flex-wrap: wrap;
  align-content: flex-end;
  background-color: orange;
  margin: 10px;
  width: 90px;
  height: 500px;
}

Try it on StackBlitz

We used the flex-end value to align the flexbox's lines to the cross-end edge of the <section>'s cross-axis.

What is align-content: space-between in CSS Flexbox?

space-between does the following:

• It aligns the flexbox's first line with the main-start edge of the flexible container's main axis.
• It aligns the flexbox's last line with the main-end side of the flexible container's main axis.
• It creates equal spacing between each pair of lines between the first and last line.

space-between creates equal spacing between each pair of lines between the first and last line

Here's an example:

section {
  display: flex;
  flex-wrap: wrap;
  align-content: space-between;
  background-color: orange;
  margin: 10px;
  width: 90px;
  height: 500px;
}

Try it on StackBlitz

The snippet above used the space-between value to create equal spacing between each pair of lines between the first and last line.

What is align-content: space-around in CSS Flexbox?

space-around assigns equal spacing to each side of a flexible container's lines.

Therefore, the space before the first line and after the last one is half the width of the space between each pair of lines.

space-around assigns equal spacing to each side of a flexible container's lines.

Here's an example:

section {
  display: flex;
  flex-wrap: wrap;
  align-content: space-around;
  background-color: orange;
  margin: 10px;
  width: 90px;
  height: 500px;
}

Try it on StackBlitz

The snippet above used the space-around value to assign equal spacing to each side of the flexible container's lines.

What is align-content: space-evenly in CSS Flexbox?

space-evenly assigns even spacing to both ends of a flexible container and between its lines.

space-evenly assigns even spacing to both ends of a flexible container and between its lines.

Here's an example:

section {
  display: flex;
  flex-wrap: wrap;
  align-content: space-evenly;
  background-color: orange;
  margin: 10px;
  width: 90px;
  height: 500px;
}

Try it on StackBlitz

We used the space-evenly value to assign even spacing to both ends of the flexbox and between its lines.

So, now that we know the types of CSS flexible container properties, we can discuss the flex item properties.

What Are the Flexible Item's Properties?

A flexible item's properties specify how browsers should layout a specified item within the flexible box model.

Note: We define a flexible item's property on the flex item, not its container.

The six (6) types of flex item properties are:

• align-self
• order
• flex-grow
• flex-shrink
• flex-basis
• flex

Let's discuss the six types now.

What Is Flexbox's align-self Property?

align-self specifies how browsers should position selected flexible items along the flexbox's cross-axis.

Note:

• align-self affects only the selected flexible item—not all the flexbox's items.
• align-self overrides the align-items property.

The align-self property accepts the following values:

• stretch
• flex-start
• center
• flex-end
• baseline

Let's discuss the five values.

What is align-self: stretch in CSS Flexbox?

stretch stretches the selected flexible items to fill the flexbox's cross-axis.

stretch stretches the selected flexible item(s) to fill the flexbox's cross-axis.

Here's an example:

.flex-item2 {
  align-self: stretch;
}

Try it on StackBlitz

We used the stretch value to stretch flex-item2 to fill its container's cross-axis.

What is align-self: flex-start in CSS Flexbox?

flex-start aligns the selected flexible items with the cross-start edge of the flexbox's cross-axis.

flex-start aligns the selected flexible item(s) with the cross-start edge of the flexbox's cross-axis.

Here's an example:

.flex-item2 {
  align-self: flex-start;
}

Try it on StackBlitz

The snippet above used the flex-start value to align flex-item2 to the cross-start edge of its container's cross-axis.

What is align-self: center in CSS Flexbox?

center aligns the selected flexible items to the center of the flexbox's cross-axis.

center aligns the selected flexible item(s) to the center of the flexbox's cross-axis.

Here's an example:

.flex-item2 {
  align-self: center;
}

Try it on StackBlitz

The snippet above used the center value to align flex-item2 to the center of its container's cross-axis.

What is align-self: flex-end in CSS Flexbox?

flex-end aligns the selected flexible items with the cross-end edge of the flexbox's cross-axis.

flex-end aligns the selected flexible item(s) with the cross-end edge of the flexbox's cross-axis.

Here's an example:

.flex-item2 {
  align-self: flex-end;
}

Try it on StackBlitz

The snippet above used the flex-end value to align flex-item2 to the cross-end edge of its container's cross-axis.

What is align-self: baseline in CSS Flexbox?

baseline aligns the selected flexible items with the baseline of the flexbox's cross-axis.

Here's an example:

.flex-item2 {
  font-size: 3rem;
  align-self: baseline;
}

Try it on StackBlitz

We used the baseline value to align flex-item2 to its container's baseline.

Let's now discuss the second type of flexible item property.

What Is Flexbox's order Property?

order changes a flexible item's default order (arrangement).

In other words, order allows you to reposition a flexbox's item without altering your HTML code's layout.

Here's an example:

<ul style="display: flex; flex-direction: column">
  <li style="order: 6">1</li>
  <li style="order: 4">2</li>
  <li style="order: 1">3</li>
  <li style="order: 7">4</li>
  <li style="order: 2">5</li>
  <li style="order: 5">6</li>
  <li style="order: 3">7</li>
</ul>

Try it on StackBlitz

The HTML snippet above used the order property to change the unordered list's arrangement.

So, instead of the following order:

• 1
• 2
• 3
• 4
• 5
• 6
• 7

The browser will display this:

• 3
• 5
• 7
• 2
• 6
• 1
• 4

Use the order property with caution, as it prevents screen readers from accessing the correct reading order of an HTML document. Only use it if it is super important to use CSS to change the HTML code's layout.

But in most cases, it is best to rearrange the HTML code directly rather than using CSS.

Note: The style="value" syntax, in the HTML snippet above, is the inline CSS technique for styling HTML elements.

What Is Flexbox's flex-grow Property?

flex-grow tells browsers how much of the flexbox's left-over space they should add to the selected flexible item's size.

Note: A left-over space refers to the space remaining after browsers have deducted the sum of all flexible items' sizes from the flexbox's size.

Here's an example:

.flex-item3 {
  flex-grow: 0.5;
}

<section>
  <div class="flex-item1">1</div>
  <div class="flex-item2">2</div>
  <div class="flex-item3">3</div>
  <div class="flex-item4">4</div>
</section>

Try it on StackBlitz

We used the flex-grow property to make browsers add half of <section>'s left-over space to flex-item3's size.

Note: flex-grow's default value is 0.

What Is Flexbox's flex-shrink Property?

flex-shrink tells browsers how much the specified flexible item should shrink when the sum of all items' sizes exceeds the flexbox's size.

In other words, suppose the flexbox's size is insufficient to fit the flexible items. In that case, browsers will shrink the items to fit the container.

Therefore, flex-shrink allows you to specify the shrinking factor of a flexible item.

Here's an example:

.flex-item3 {
  flex-shrink: 0;
}

Try it on StackBlitz

We used the flex-shrink property to prevent browsers from shrinking flex-item3.

Note:

• Browsers will not shrink flexible items with a flex-shrink value of 0.
• flex-shrink's default value is 1.

What Is Flexbox's flex-basis Property?

flex-basis sets the initial length of a flexible item.

Here's an example:

.flex-item3 {
  flex-basis: 100px;
}

Try it on StackBlitz

We used the flex-basis property to set flex-item3's initial length to 100px.

Note the following:

• auto is flex-basis' default value.
• A flex-basis' value (other than auto) has higher specificity than width (or height). Therefore, suppose you define both for a flexible item. In that case, browsers will use flex-basis.
• The flex-basis property sets the content box's initial width. But you can use the box-sizing property to make it set the border box's width instead.

What Is Flexbox's flex Property?

flex is a shorthand for the flex-grow, flex-shrink, and flex-basis properties.

In other words, instead of writing:

.flex-item3 {
  flex-grow: 0.5;
  flex-shrink: 0;
  flex-basis: 100px;
}

You can alternatively use the flex property to shorten your code like so:

.flex-item3 {
  flex: 0.5 0 100px;
}

Note the following:

• flex: auto is equivalent to flex: 1 1 auto.
• flex: none is equivalent to flex: 0 0 auto.
• flex: initial sets the flex property to its default value. It is equivalent to flex: 0 1 auto.
• flex: inherit inherits its parent element's flex property's values.

So, now that we know the flexbox properties developers use to layout flexible boxes and their direct children, we can discuss how to center elements with flexbox.

How to Center Elements Horizontally with Flexbox

You can center any element horizontally within its container by:

• Setting its container's display property to flex
• Setting the flexible container's justify-content property to center

Here's an example:

section {
  display: flex;
  justify-content: center;
  background-color: orange;
  width: 100%;
  height: 400px;
}

Try it on StackBlitz

How to Center Elements Vertically with Flexbox

You can center any element vertically within its container by:

• Setting its container's display property to flex
• Setting the flexible container's align-items property to center

Here's an example:

section {
  display: flex;
  align-items: center;
  background-color: orange;
  width: 100%;
  height: 400px;
}

Try it on StackBlitz

How to Center Elements Horizontally and Vertically with Flexbox

You can center any HTML element horizontally and vertically within its container by:

• Setting its container's display property to flex
• Setting the flexible container's justify-content and align-items properties to center

Here's an example:

section {
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: orange;
  width: 100%;
  height: 400px;
}

Try it on StackBlitz

Overview

In this article, we discussed all the Flexbox tools you need to create basic and advanced website layouts in flexible and responsive ways.

Thanks for reading!

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