CSS3 Flexible Box

CSS3 Flexbox

Flexible boxes, or flexbox, is a new layout mode in CSS3.

Use of flexbox ensures that elements behave predictably when the page layout must accommodate different screen sizes and different display devices.

For many applications, the flexible box model provides an improvement over the block model in that it does not use floats, nor do the flex container's margins collapse with the margins of its contents.

Browser Support

The numbers in the table specify the first browser version that fully supports the feature.

Numbers followed by -webkit- or -moz- specify the first version that worked with a prefix.

Basic support (single-line flexbox)	11.0	29.0 21.0 -webkit-	22.0 18.0 -moz-	6.1 -webkit-	12.1 -webkit-
Multi-line flexbox	11.0	29.0 21.0 -webkit-	28.0	6.1 -webkit-	17.0 15.0 -webkit- 12.1

CSS3 Flexbox Concepts

Flexbox consists of flex containers and flex items.

A flex container is declared by setting the display property of an element to either flex (rendered as a block) or inline- flex (rendered as inline).

Inside a flex container there is one or more flex items.

Note: Everything outside a flex container and inside a flex item is rendered as usual. Flexbox defines how flex items are laid out inside a flex container.

Flex items are positioned inside a flex container along a flex line. By default there is only one flex line per flex container.

The following example shows three flex items. They are positioned by default: along the horizontal flex line, from left to right:

It is also possible to change the direction of the flex line.

If we set the direction property to rtl (right-to- left), the text is drawn right to left, and also the flex line changes direction, which will change the page layout:

Flex Direction

The flex-direction property specifies the direction of the flexible items inside the flex container. The default value of flex-direction is row (left-to-right, top-to- bottom).

The other values are as follows:

• row-reverse - If the writing-mode (direction) is left to right, the flex items will be laid out right to left
• column - If the writing system is horizontal, the flex items will be laid out vertically
• column-reverse - Same as column, but reversed

The following example shows the result of using the row-reverse value:

The following example shows the result of using the column value:

The following example shows the result of using the column- reverse value:

The justify-content Property

The justify-content property horizontally aligns the flexible container's items when the items do not use all available space on the main- axis.

The possible values are as follows:

• flex-start - Default value. Items are positioned at the beginning of the container
• flex-end - Items are positioned at the end of the container
• center - Items are positioned at the center of the container
• space-between - Items are positioned with space between the lines
• space-around - Items are positioned with space before, between, and after the lines

The following example shows the result of using the flex-end value:

The following example shows the result of using the center value:

The following example shows the result of using the space- between value:

The following example shows the result of using the space-around value:

The align-items Property

The align-items property vertically aligns the flexible container's items when the items do not use all available space on the cross- axis.

The possible values are as follows:

• stretch - Default value. Items are stretched to fit the container
• flex-start - Items are positioned at the top of the container
• flex-end - Items are positioned at the bottom of the container
• center - Items are positioned at the center of the container (vertically)
• baseline - Items are positioned at the baseline of the container

The following example shows the result of using the stretch value (this is the default value):

The following example shows the result of using the flex-start value:

The following example shows the result of using the flex-end value:

The following example shows the result of using the center value:

The following example shows the result of using the baseline value:

The flex-wrap Property

The flex-wrap property specifies whether the flex items should wrap or not, if there is not enough room for them on one flex line.

The possible values are as follows:

• nowrap - Default value. The flexible items will not wrap
• wrap - The flexible items will wrap if necessary
• wrap-reverse - The flexible items will wrap, if necessary, in reverse order

The following example shows the result of using the nowrap value (this is the default value):

The following example shows the result of using the wrap value:

The following example shows the result of using the wrap-reverse value:

The align-content Property

The align-content property modifies the behavior of the flex-wrap property. It is similar to align-items, but instead of aligning flex items, it aligns flex lines.

The possible values are as follows:

• stretch - Default value. lines stretch to take up the remaining space
• flex-start - lines are packed toward the start of the flex container
• flex-end - lines are packed toward the end of the flex container
• center - lines are packed toward the center of the flex container
• space-between - lines are evenly distributed in the flex container
• space-around - lines are evenly distributed in the flex container, with half-size spaces on either end

The following example shows the result of using the center value:

Flex Item Properties

Ordering

The order property specifies the order of a flexible item relative to the rest of the flexible items inside the same container:

Margin

Setting margin: auto; will absorb extra space. It can be used to push flex items into different positions.

In the following example we set margin-right: auto; on the first flex item. This will cause all the extra space to be absorbed to the right of that element:

Perfect Centering

In the following example we will solve an almost daily problem: perfect centering.

It is very easy with flexbox. Setting margin: auto; will make the item perfectly centered in both axis:

align-self

The align-self property of flex items overrides the flex container's align-items property for that item. It has the same possible values as the align-items property.

The following example sets different align-self values to each flex item:

flex

The flex property specifies the length of the flex item, relative to the rest of the flex items inside the same container.

In the following example, the first flex item will consume 2/4 of the free space, and the other two flex items will consume 1/4 of the free space each:

CSS3 Flexbox Properties

The following table lists the CSS properties used with flexbox:

CSS3 Media Queries

CSS2 Introduced Media Types

The @media rule, introduced in CSS2, made it possible to define different style rules for different media types.

Examples: You could have one set of style rules for computer screens, one for printers, one for handheld devices, one for television-type devices, and so on.

Unfortunately these media types never got a lot of support by devices, other than the print media type.

CSS3 Introduces Media Queries

Media queries in CSS3 extend the CSS2 media types idea: Instead of looking for a type of device, they look at the capability of the device.

Media queries can be used to check many things, such as:

• width and height of the viewport
• width and height of the device
• orientation (is the tablet/phone in landscape or portrait mode?)
• resolution

Using media queries are a popular technique for delivering a tailored style sheet to tablets, iPhone, and Androids.

Browser Support

The numbers in the table specifies the first browser version that fully supports the @media rule.

Rule
@media	21	9	3.5	4.0	9

Media Query Syntax

A media query consists of a media type and can contain one or more expressions, which resolve to either true or false.

The result of the query is true if the specified media type matches the type of device the document is being displayed on and all expressions in the media query are true. When a media query is true, the corresponding style sheet or style rules are applied, following the normal cascading rules.

Unless you use the not or only operators, the media type is optional and the all type will be implied.

You can also have different stylesheets for different media:

CSS3 Media Types

Media Queries Simple Examples

One way to use media queries is to have an alternate CSS section right inside your style sheet.

The following example changes the background-color to lightgreen if the viewport is 480 pixels wide or wider (if the viewport is less than 480 pixels, the background-color will be pink):

The following example shows a menu that will float to the left of the page if the viewport is 480 pixels wide or wider (if the viewport is less than 480 pixels, the menu will be on top of the content):

CSS3 @media Reference

For a full overview of all the media types and features/expressions, please look at the @media rule in CSS reference.

CSS3 Media Queries - Examples

CSS3 Media Queries - More Examples

Let us look at some more examples of using media queries.

We will start with a list of names which function as email links. The HTML is:

Notice the data-email attribute. In HTML5, we can use attributes prefixed with data- to store information. We will use the data- attribute later.

Width from 520 to 699px - Apply an email icon to each link

When the browser's width is between 520 and 699px, we will apply an email icon to each email link:

Width from 700 to 1000px - Preface the links with a text

When the browser's width is between from 700 to 1000px, we will preface each email link with the text "Email:";

Width above 1001px - Apply email address to links

When the browser's width is above 1001px, we will append the email address to the links.

We will use the value of the data- attribute to add the email address after the person's name:

Width above 1151px - Add icon as we used before

For browser widths above 1151px, we will again add the icon as we used before.

Here, we do not have to write an additional media query block, we can just append an additional media query to our already existing one using a comma (this will behave like an OR operator):