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<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>CSS Flexible Box Layout Module</title>
<link rel="stylesheet" type="text/css" href="http://dev.w3.org/csswg/default.css">
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED">
<style>
code.one-line { white-space: pre; }
.code-and-figure {
display: table;
margin: 0 auto;
border-spacing: 1em;
}
.code-and-figure > div {
display: table-cell;
vertical-align: middle;
}
:not(code) var { font-style: normal; color: #005A9C; }
</style>
</head><body>
<div class="head">
<!--logo-->
<h1 id="head-box-flexible">CSS Flexible Box Layout Module</h1>
<h2 class="no-num no-toc" id="w3c-working">[LONGSTATUS], [DATE]</h2>
<dl>
<dt>This version:
<!--<dd><a href="[VERSION]">http://www.w3.org/TR/[YEAR]/WD-css3-flexbox-[CDATE]/</a>-->
<dd><a href="http://dev.w3.org/csswg/[SHORTNAME]/">http://dev.w3.org/csswg/[SHORTNAME]/</a>
<dt>Latest version:
<!--<dd><a href="[LATEST]">[LATEST]</a>-->
<dd><a href="http://www.w3.org/TR/css3-flexbox/">http://www.w3.org/TR/css3-flexbox/</a>
<dt>Editor's Draft:
<dd><a href="http://dev.w3.org/csswg/css3-flexbox/">http://dev.w3.org/csswg/css3-flexbox/</a>
<dt>Previous versions:
<dd><a href="http://www.w3.org/TR/2012/WD-css3-flexbox-20120322/">http://www.w3.org/TR/2012/WD-css3-flexbox-20120322/</a>
<dd><a href="http://www.w3.org/TR/2011/WD-css3-flexbox-20111129/">http://www.w3.org/TR/2011/WD-css3-flexbox-20111129/</a>
<dd><a href="http://www.w3.org/TR/2011/WD-css3-flexbox-20110322/">http://www.w3.org/TR/2011/WD-css3-flexbox-20110322/</a>
<dd><a href="http://www.w3.org/TR/2009/WD-css3-flexbox-20090723/">http://www.w3.org/TR/2009/WD-css3-flexbox-20090723/</a>
<dt>Issues List:
<dd><a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=CSS&component=Flexbox&resolution=---">Bugzilla Bugs for Flexbox</a>
<dt>Discussion:
<dd><a href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a> with subject line "<code>[css3-flexbox] …message topic…</code>"
<dt>Editors:
<dd><a href="http://www.xanthir.com/contact">Tab Atkins Jr.</a>, Google Inc.
<dd>Alex Mogilevsky, Microsoft Corporation, <a href="mailto:alexmog@microsoft.com">alexmog@microsoft.com</a>
<dd>L. David Baron, Mozilla Corporation, <a href="mailto:dbaron@dbaron.org">dbaron@dbaron.org</a>
<dt>Authors and former editors:
<dd>Neil Deakin, Mozilla Corporation, <a href="mailto:enndeakin@gmail.com">enndeakin@gmail.com</a>
<dd>Ian Hickson, formerly of Opera Software, <a href="mailto:ian@hixie.ch">ian@hixie.ch</a>
<dd>David Hyatt, formerly of Netscape Corporation, <a href="mailto:hyatt@apple.com">hyatt@apple.com</a>
</dl>
<!--copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id="abstract">
Abstract</h2>
<p>The specification describes a CSS box model optimized for user interface design. In the flexbox layout model, the children of a flexbox can be laid out in any direction, and can "flex" their sizes, either growing to fill unused space or shrinking to avoid overflowing the parent. Both horizontal and vertical alignment of the children can be easily manipulated. Nesting of these boxes (horizontal inside vertical, or vertical inside horizontal) can be used to build layouts in two dimensions.
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<!--status-->
<p>
The following features are at-risk:
<ul>
<li>Flexbox pagination rules
</ul>
<h2 class="no-num no-toc" id="table">Table of contents</h2>
<!--toc-->
<h2 id="intro">
Introduction</h2>
<p><em>This section is not normative.</em>
<p>CSS 2.1 defined four layout modes — algorithms which determine the size and position of boxes based on their relationships with their sibling and ancestor boxes: block layout, designed for laying out documents; inline layout, designed for laying out text; table layout, designed for laying out information in a tabular format; and positioned layout, designed for very explicit positioning without much regard for other elements in the document. This module introduces a new layout mode, flexbox layout, which is designed for laying out more complex applications and webpages.
<p>Flexbox layout is superficially similar to block layout. It lacks many of the more complex text or document-formatting properties that can be used in block layout, such as 'float' and 'columns', but in return it gains more simple and powerful tools for aligning its contents in ways that webapps and complex web pages often need.
<p>The contents of a flexbox can be laid out in any direction (left, right, down, or even up!), can have their order swapped around dynamically (i.e., display order is independent of source order), and can "flex" their sizes and positions to respond to the available space. If a flexbox is <i>multi-line</i>, the flexbox items flow in two dimensions, wrapping into separate lines in a fashion similar to how text is wrapped into multiple lines.
<div class="example">
<p>For example, the following HTML snippet uses flexbox to create a toolbar with icons. The flexbox is horizontal, and the children's widths don't fill the flexbox's width, so the additional space is distributed around and between the children. As the flexbox grows (perhaps because the user is viewing the page on a wider screen), the children spread out evenly and automatically:
<pre>
<ul>
<li><button><img src='new.svg' alt="New"></button></li>
<li><button><img src='upload.svg' alt="Upload"></button></li>
<li><button><img src='save.svg' alt="Save"></button></li>
<li><button><img src='trash.svg' alt="trash"></button></li>
</ul>
<style>
ul { display: flex; flex-pack: distribute; }
/* Irrelevant styling for this example removed. */
</style></pre>
<div class='figure'>
<img src="images/toolbar-example.svg" width=400 height=140 alt>
<p class='caption'>Example rendering of the above code snippet, at two different flexbox widths.
</div>
</div>
<h3 id="placement">
Module interactions</h3>
<p>This module extends the definition of the 'display' property.
<h3 id="values">
Values</h3>
<p>This specification follows the <a href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property definition conventions</a> from [[!CSS21]]. Value types not defined in this specification are defined in CSS Level 2 Revision 1 [[!CSS21]]. Other CSS modules may expand the definitions of these value types: for example [[CSS3VALUES]], when combined with this module, expands the definition of the <length> value type as used in this specification.
<p>In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the <a href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">''inherit''</a> keyword as their property value. For readability it has not been repeated explicitly.
<h2 id='box-model'>
The Flexbox Box Model</h2>
<p>An element with ''display:flex'' or ''display:inline-flex'' is a <dfn>flexbox</dfn>. Children of a flexbox are called <i>flexbox items</i> and are laid out using the flexbox box model.
<p>Unlike block layout, which is normally biased towards laying things out vertically, and inline layout, which is normally biased toward laying things out horizontally, the flexbox layout algorithm is agnostic as to the direction the flexbox happens to be laid out in. To make it easier to talk about flexbox layout in a general way, we will define several direction-agnostic terms here to make the rest of the spec easier to read and understand.
<div class='figure'>
<img src='images/flex-direction-terms.svg' width=510 height=300 alt>
<p class='caption'>An illustration of the various directions and sizing terms used in this specification, respectively for ''row'' and ''column'' flexboxes.
</div>
<p>
The <dfn>main axis</dfn> of a flexbox is the axis along which <i>flexbox items</i> are laid out.
The <i>flexbox items</i> are ordered
such that they start on the <dfn>main-start</dfn> side of the flexbox,
and go toward the <dfn>main-end</dfn> side.
A <i>flexbox item's</i> width or height,
whichever is in the <i>main dimension</i>,
is the item's <dfn>main size</dfn>.
The <i>flexbox item's</i> <dfn>main size property</dfn> is
either the 'width' or 'height' property,
whichever is in the <i>main dimension</i>.
<p>
The axis perpendicular to the <i>main axis</i> is called the <dfn>cross axis</dfn>,
and similarly has <dfn>cross-start</dfn> and <dfn>cross-end</dfn> directions and sides defined.
The width or height of a <i>flexbox item</i>,
whichever is in the <i>cross dimension</i>,
is the item's <dfn>cross size</dfn>,
and similarly the <dfn>cross size property</dfn> is
whichever of 'width' or 'height' that is in the <i>cross dimension</i>.
<p>
The contents of a flexbox can be easily and powerfully manipulated with a handful of properties.
Most significantly,
<i>flexbox items</i> can "flex" their <i>main size</i> by using the 'flex' property.
This "flexing" allows the items to get bigger or smaller based on the available space in the page.
If there is leftover space in the flexbox after all of the <i>flexbox items</i> have finished flexing,
the items can be aligned, centered, or distributed with the 'flex-pack' property.
<i>Flexbox items</i> can also be completely rearranged within the flexbox with the 'flex-order' property.
<p>
In the <i>cross axis</i>,
<i>flexbox items</i> can either "stretch" to fill the available space
or be aligned within the space with the 'flex-align' property.
If a flexbox is <i>multi-line</i>,
new lines are added in the <i>cross-end</i> direction,
and can similarly be aligned, centered, or distributed
within the flexbox with the 'flex-line-pack' property.
<h2 id='display-flexbox'>
Flexboxes: the ''flex'' and ''inline-flex'' 'display' values</h2>
<table class="propdef">
<tr>
<th>Name:
<td>display
<tr>
<th><a href="#values">New value</a>:
<td><dfn id='display-flex'>flex</dfn> | <dfn id='display-inline-flex'>inline-flex</dfn>
</table>
<p>
An element whose computed 'display' is either ''flex'' or ''inline-flex''
is a flexbox,
and establishes a new <dfn>flexbox formatting context</dfn> for its contents.
This is similar to a block formatting context root:
floats do not intrude into the flexbox,
and the flexbox's margins do not collapse with the margins of its contents.
Additionally,
each of the <i>flexbox items</i> establishes a new formatting context for its contents.
<p>
The ''flex'' value makes the flexbox a block-level element.
The ''inline-flex'' value makes the flexbox an atomic inline-level element.
<p>
Flexboxes are not block containers,
and so some properties that were designed with the assumption of block layout don't apply in a flexbox context.
In particular:
<ul>
<li>
all of the 'column-*' properties in the Multicol module have no effect on a flexbox.
<li>
'float' and 'clear' have no effect on a <i>flexbox item</i>.
Using 'float' on an element still causes that element's 'display' property to compute to ''block'',
and thus 'float' may affect whether an element becomes a flexbox item
or is wrapped in one.
(See <a href="http://www.w3.org/TR/CSS2/visuren.html#dis-pos-flo">CSS 2.1 Chapter 9.7</a>.)
<li>
'vertical-align' has no effect on the alignment of a flexbox item in the flexbox
</ul>
<p>
If an element's specified value for 'display' is ''inline-flex''
and the element is floated or absolutely positioned,
the computed value of 'display' is ''flex''.
The table in <a href="http://www.w3.org/TR/CSS2/visuren.html#dis-pos-flo">CSS 2.1 Chapter 9.7</a> is thus amended
to contain an additional row,
with ''inline-flex'' in the "Specified Value" column
and ''flex'' in the "Computed Value" column.
<p>
The baseline of a flexbox is:
<ul>
<li>
If any of the <i>flexbox items</i> on the flexbox's first line
(after reordering with 'flex-order')
have a computed value of ''baseline'' for 'flex-item-align',
the flexbox's baseline is the baseline of those <i>flexbox items</i>.
<li>
Otherwise, if the flexbox has at least one <i>flexbox item</i>,
and the baseline of its first <i>flexbox item</i>
(after reordering with 'flex-order')
is parallel to the flexbox's <i>main-axis</i>,
the flexbox's baseline is the baseline of its first <i>flexbox item</i>.
<li>
Otherwise, the flexbox's baseline is the "after" edge of its content box.
</ul>
<h2 id='flex-items'>
Flexbox Items</h2>
<p>
The flexbox layout algorithm operates on boxes generated by <dfn title="flexbox item|flexbox items|flexbox item's" id="flexbox-item">flexbox items</dfn>.
A <i>flexbox item</i> is:
<ol>
<li>
A block-level child of a flexbox element
<li>
An atomic inline-level child of a flexbox element
<li>
An anonymous block element wrapped around a contiguous run of non-replaced inline child elements.
However, if the contents of the anonymous block would be solely an anonymous inline containing only whitespace,
the box is not generated,
as if it had ''display:none''.
</ol>
<p>
Some values of 'display' trigger the generation of anonymous boxes.
For example, a ''table-cell'' child of a block container is fixed up by generating ''table'' and ''table-row'' elements around it.
This fixup must occur <em>before</em> a flexbox's contents are checked to see if it's necessary to generate anonymous flexbox items.
<p class='note'>
In the future, other kinds of fixup such as ''display:run-in'' or ''display:ruby'' should also run before flexbox fixup.
<div class="example">
<p>Examples of flexbox items:
<pre>
<div style="display:flex">
<!-- flexbox item: block-level child -->
<div id="item1">block</div>
<!-- not a flexbox item, because it's out-of-flow -->
<!-- however, an anonymous flexbox item is wrapped around
the placeholder it leaves behind-->
<div id="not-an-item2" style="position: absolute;">block</div>
<!-- flexbox item: block-level child -->
<div id="item3" style="display:table">table</div>
<!-- flexbox item: anonymous table wrapped around table-cell -->
<div id="item4" style="display:table-cell">table-cell</div>
<!-- flexbox item: anonymous block box around inline content -->
anonymous item 5
<!-- flexbox item: block-level child -->
<div id="item6">block</div>
<!-- flexbox item: anonymous block around inline content -->
anonymous item 7.1
<span id="item7.1">
text 7.2
<div id="not-an-item7.3">block</div>
text 7.4
</span>
<!-- flexbox item: block-level replaced element -->
<iframe id="item8" style="display:block;"></iframe>
<!-- flexbox item: inline-level replaced element -->
<img id="item9">
<!-- flexbox item: atomic inline-level element -->
<button id="item10">button</button>
<!-- flexbox item: inline-table -->
<div id="item11" style="display:inline-table">table</div>
<!-- flexbox item: floated inline, which changes to a block -->
<span id="item12" style="float: left;">span</span>
</div></pre>
<p>
Notice that block element "not-an-item7.3" is not a separate flexbox item,
because it is contained inside an inline element which is being wrapped into an anonymous flexbox item.
Similarly,
the block element "not-an-item2" is not a flexbox item,
because it's absolutely positioned and thus out of flow.
</div>
<p>
The computed value for 'display' for elements that are <i>flexbox items</i>
must be determined by applying the table in <a href="http://www.w3.org/TR/CSS2/visuren.html#dis-pos-flo">CSS 2.1 Chapter 9.7</a>.
<h3 id='abspos-flexbox-items'>
Absolutely Positioned Flexbox Children</h3>
<p>
Absolutely positioned children of a flexbox are not <i>flexbox items</i>,
but they leave behind "placeholders" in their normal position in the box tree.
These placeholders are anonymous inline boxes with a width and height of ''0px'',
and they interact normally with the flexbox layout algorithm.
In particular,
they'll trigger the creation an anonymous flexbox item wrapper boxes,
or join neighboring inline elements in <em>their</em> anonymous flexbox item wrapper boxes.
<p>
The "static position" of an absolutely positioned child of a flexbox
(the position when the 'top'/'right'/'bottom'/'left' properties are ''auto''),
then,
is the final position of its corresponding placeholder, after flexbox layout has been performed.
<p class='note'>
Note: In most cases,
this means that absolutely positioned items will have no effect on flexbox layout,
even if they force the generation of an anonymous flexbox item wrapper,
because those wrapper items will also collapse to zero size and have no effect.
The only exceptions are when the flexbox has ''flex-pack:justify'' or ''flex-pack:distribute'',
in which case the anonymous flexbox item will cause there to be two packing spaces where there would otherwise be only one,
resulting in a double-size space between two "real" items.
<h2 id='multi-line'>
Multi-line Flexbox</h2>
<p>
A flexbox can be either <i>single-line</i> or <i>multi-line</i>,
depending on the 'flex-wrap' property.
A <dfn>single-line</dfn> flexbox lays out all of its children in a single line,
even if that would cause the flexbox to overflow its bounds.
A <dfn>multi-line</dfn> flexbox breaks its <i>flexbox items</i> across multiple lines to avoid overflowing,
similar to how text is broken onto a new line when it gets too wide to fit on the existing line.
Every line contains at least one <i>flexbox item</i>,
unless the flexbox itself is completely empty.
<p>
When additional lines are created,
they are stacked in the flexbox along the <i>cross axis</i>.
Once content is broken into lines,
each line is laid out independently;
flexible lengths and the 'flex-pack' and 'flex-item-align' properties only consider the items on a single line at a time.
<p>
The <i>main size</i> of a line is the same as the <i>main size</i> of the flexbox's content box.
the <i>cross size</i> of a line is the minimum size necessary to contain the <i>flexbox items</i> on the line,
after aligment due to 'flex-item-align'.
The lines themselves are then aligned within the flexbox with the 'flex-line-pack' property.
<div class=example>
<p>
This example shows four buttons that do not fit horizontally.
<pre><style>
#div1 {
display: flex;
flex-flow: row wrap;
width: 300px;
}
button {
flex:80px 1;
}
<style>
<div id="div1">
<button id="button1">Elephant</button>
<button id="button2">Tiger</button>
<button id="button3">Antelope</button>
<button id="button4">Wildebeest</button>
</div></pre>
<p>
The buttons are first set to their preferred widths,
in this case 80 pixels.
This will allow the first three buttons to fit in 240 pixels with 60 pixels left over of remaining space.
Because the 'flex-flow' property specifies a multi-line flexbox
(due to the ''wrap'' keyword appearing in its value),
the flexbox will create an additional line to contain the last button.
<p>
Flexibility is applied to each element,
separately for each line.
The first line has 60 pixels of remaining space
and all of the buttons have the same flexibility,
so each of the three buttons on that line will receive 20 pixels of extra width,
ending up 100px wide.
The remaining button is on a line of its own
and will stretch to the entire width of the line, or 300 pixels.
<div style="width:300px; border:medium solid green; overflow: hidden;">
<button style="width:100px; float: left;">Elephant</button>
<button style="width:100px; float: left;">Tiger</button>
<button style="width:100px; float: left;">Antelope</button>
<button style="width:300px; float: left;">Wildebeest</button>
</div>
<p>
If the box was resized, the buttons may rearrange onto different lines as necessary.
<p>
If the style rules in the example above were changed to the following:
<pre>
#div1 {
display: flex;
flex-flow: row wrap;
flex-pack: center;
width: 300px;
}
button {
flex:80px 1;
max-width: 90px;
}</pre>
<p>
Similar to the previous example,
the first three buttons will fit on the first line,
and the last button will wrap onto a new line.
However, when the buttons attempt to flex they can only grow to 90px each,
due to their 'max-width' property.
This leaves 30px of free space on the first line
and 210px of free space on the second line.
Because 'flex-pack' is set to ''center'',
the buttons will be centered on each line,
with the free space split equally on either side.
<div style="width:300px; border:medium solid green; text-align:center;">
<button style="width:90px; float: left; margin-left: 15px;">Elephant</button>
<button style="width:90px; float: left;">Tiger</button>
<button style="width:90px; float: left;">Antelope</button>
<button style="width:90px">Wildebeest</button>
</div>
</div>
<h2>
Ordering and Orientation</h2>
<p>
The first level of flexbox functionality is the ability to lay out a flexbox's contents in any direction and in any order.
This allows an author to trivially achieve effects that would previously have required complex or fragile methods,
such as hacks using the 'float' and 'clear' properties.
This functionality is exposed through the 'flex-direction', 'flex-wrap', and 'flex-order' properties.
<h3 id='flex-direction'>
Flexbox Flow Direction: the 'flex-direction' property</h3>
<table class=propdef>
<tr>
<th>Name:</th>
<td><dfn>flex-direction</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>row | row-reverse | column | column-reverse
<tr>
<th>Initial:
<td>row
<tr>
<th>Applies To:
<td>flexboxes
<tr>
<th>Inherited:
<td>no
<tr>
<th>Computed Value:
<td>specified value
<tr>
<th>Media:
<td>visual
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical Order:
<td><abbr title="follows order of property value definition">per grammar</abbr>
</table>
<p>
The 'flex-direction' property specifies how <i>flexbox items</i> are placed in the flexbox,
by setting the direction of the flexbox's <i>main axis</i>.
This determines the direction that flexbox items are laid out in.
<dl>
<dt><dfn id='flex-flow-row'>''row''</dfn>
<dd>
The flexbox's <i>main axis</i> has the same orientation as the inline axis of the current <a href="http://www.w3.org/TR/css3-writing-modes/#writing-mode">writing mode</a>
(the primary direction that text is laid out in).
The <i>main-start</i> and <i>main-end</i> directions are equivalent to the <a href="http://www.w3.org/TR/css3-writing-modes/#start">start</a> and <a href="http://www.w3.org/TR/css3-writing-modes/#end">end</a> directions, respectively,
of the current <a href="http://www.w3.org/TR/css3-writing-modes/#writing-mode">writing mode</a>.
<dt><dfn id='flex-flow-row-reverse'>''row-reverse''</dfn>
<dd>
Same as ''row'',
except the <i>main-start</i> and <i>main-end</i> directions are swapped.
<dt><dfn id='flex-flow-column'>''column''</dfn>
<dd>
The flexbox's <i>main axis</i> has the same orientation as the block axis of the current <a href="http://www.w3.org/TR/css3-writing-modes/#writing-mode">writing mode</a>
(the primary direction that blocks are laid out in).
The <i>main-start</i> and <i>main-end</i> directions are equivalent to the <a href="http://www.w3.org/TR/css3-writing-modes/#before">before</a> and <a href="http://www.w3.org/TR/css3-writing-modes/#after">after</a> directions, respectively,
of the current <a href="http://www.w3.org/TR/css3-writing-modes/#writing-mode">writing mode</a>.
<dt><dfn id='flex-flow-column-reverse'>''column-reverse''</dfn>
<dd>
Same as ''column'',
except the <i>main-start</i> and <i>main-end</i> directions are swapped.
</dl>
<h3 id='flex-wrap'>
Flexbox Wrapping: the 'flex-wrap' prop
B74
erty</h3>
<table class=propdef>
<tr>
<th>Name:</th>
<td><dfn>flex-wrap</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>nowrap | wrap | wrap-reverse
<tr>
<th>Initial:
<td>nowrap
<tr>
<th>Applies To:
<td>flexboxes
<tr>
<th>Inherited:
<td>no
<tr>
<th>Computed Value:
<td>specified value
<tr>
<th>Media:
<td>visual
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical Order:
<td><abbr title="follows order of property value definition">per grammar</abbr>
</table>
<p>
The 'flex-wrap' property controls whether the flexbox is <i>single-line</i> or <i>multi-line</i>,
and the direction of the <i>cross-axis</i>,
which determines the direction new lines are stacked in.
<dl>
<dt><dfn id='flex-flow-nowrap'>''nowrap''</dfn>
<dd>
The flexbox is <i>single-line</i>.
The <i>cross-start</i> direction is equivalent to either
the <a href="http://www.w3.org/TR/css3-writing-modes/#start">start</a>
or <a href="http://www.w3.org/TR/css3-writing-modes/#before">before</a>
direction of the current <a href="http://dev.w3.org/csswg/css3-writing-modes/#writing-mode">writing mode</a>,
whichever is in the <i>cross axis</i>,
and the <i>cross-end</i> direction is the opposite direction of <i>cross-start</i>.
<dt><dfn id='flex-flow-wrap'>''wrap''</dfn>
<dd>
The flexbox is <i>multi-line</i>.
The <i>cross-start</i> direction is equivalent to either
the <a href="http://www.w3.org/TR/css3-writing-modes/#start">start</a>
or <a href="http://www.w3.org/TR/css3-writing-modes/#before">before</a>
direction of the current <a href="http://dev.w3.org/csswg/css3-writing-modes/#writing-mode">writing mode</a>,
whichever is in the <i>cross axis</i>,
and the <i>cross-end</i> direction is the opposite direction of <i>cross-start</i>.
<dt><dfn id='flex-flow-wrap-reverse'>''wrap-reverse''</dfn>
<dd>
Same as ''wrap'',
except the <i>cross-start</i> and <i>cross-end</i> directions are swapped.
</dl>
<h3 id='flex-flow'>
Flex Direction and Wrap: the 'flex-flow' shorthand</h3>
<table class=propdef>
<tr>
<th>Name:</th>
<td><dfn>flex-flow</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><'flex-direction'> || <'flex-wrap'>
<tr>
<th>Initial:
<td>see individual properties
<tr>
<th>Applies To:
<td>flexboxes
<tr>
<th>Inherited:
<td>see individual properties
<tr>
<th>Computed Value:
<td>see individual properties
<tr>
<th>Media:
<td>visual
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical Order:
<td><abbr title="follows order of property value definition">per grammar</abbr>
</table>
<p>The 'flex-flow' property is a shorthand for setting the 'flex-direction' and 'flex-wrap' properties together.
<div class="example">
<p>Some examples of valid flows:
<table style="margin: 0 auto; vertical-align: middle; border-spacing: 2em 1em;">
<tr>
<td><pre>
div { flex-flow: row; }
/* Initial value. Main-axis is
inline, no wrap. */</pre>
<td><img src='images/flex-flow1.svg' width=240 height=80 alt>
<tr>
<td><pre>
div { flex-flow: column wrap; }
/* Main-axis is block-direction and lines
wrap in the inline direction. For an
English page, the main-axis is top-to-bottom
and lines wrap to the right. */</pre>
<td><img src='images/flex-flow2.svg' width=170 height=200 alt>
<tr>
<td><pre>
div { writing-mode: vertical-rl;
flex-flow: column wrap-reverse; }
/* Main-axis is block direction (right to
left). New lines wrap upwards. */</pre>
<td><img src='images/flex-flow3.svg' width=200 height=170 alt>
</table>
</div>
<h3 id='flex-order'>
Display Order: the 'flex-order' property</h3>
<p><i>Flexbox items</i> are, by default, displayed and laid out in the same order as they appear in the source document. The 'flex-order' property may be used to change this ordering.
<table class=propdef>
<tr>
<th>Name:
<td><dfn>flex-order</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><number>
<tr>
<th>Initial:
<td>0
<tr>
<th>Applies to:
<td><i>flexbox items</i></td>
<tr>
<th>Inherited:
<td>no
<tr>
<th>Computed value:
<td>specified value
<tr>
<th>Media:
<td>visual
<tr>
<th>Animatable:
<td>yes
<tr>
<th>Canonical Order:
<td><abbr title="follows order of property value definition">per grammar</abbr>
</table>
<p>The 'flex-order' property assigns <i>flexbox items</i> to ordinal groups.
<p>Ordinal groups control the order in which <i>flexbox items</i> appear. A flexbox will lay out its content starting from the lowest numbered ordinal group and going up. Items with the same ordinal group are laid out in the order they appear in the source document. 'flex-order' has no effect on stacking/layering; elements must still be drawn over/under each other based on document order, 'z-index', and other relevant means.
<div class='example'>
<p>The following figure shows a simple tabbed interface, where the tab for the active pane is always in front:
<div class='figure'><img src="images/flex-order-example.png" alt></div>
<p>This could be implemented with the following CSS (showing only the flexbox-relevant code):
<pre>
.tabs {
display: flex;
}
.tabs > .current {
flex-order: -1; /* Lower than the default of 0 */
}</pre>
</div>
<div class='example'>
<p>Many web pages have a similar shape in the markup, with a header on top, a footer on bottom, and then a content area and one or two additional columns in the middle. Generally, it's desirable that the content come first in the page's source code, before the additional columns. However, this makes many common designs, such as simply having the additional columns on the left and the content area on the right, difficult to achieve. This has been addressed in many ways over the years, often going by the name "Holy Grail Layout" when there are two additional columns. 'flex-order' makes this trivial. For example, take the following sketch of a page's code and desired layout:
<div class='code-and-figure'>
<div><pre>
<!DOCTYPE html>
<header>...</header>
<div id='main'>
<article>...</article>
<nav>...</nav>
<aside>...</aside>
</div>
<footer>...</footer></pre></div>
<div><img src="images/flex-order-page.svg" width=400 height=360 alt="In this page the header is at the top and the footer at the bottom, but the article is in the center, flanked by the nav on the right and the aside on the left."></div>
</div>
<p>This layout can be easily achieved with Flexbox:
<pre>
#main { display: flex; }
#main > article { flex:1; flex-order: 2; }
#main > nav { width: 200px; flex-order: 1; }
#main > aside { width: 200px; flex-order: 3; }</pre>
<p>As an added bonus, the columns will all be equal-height by default, and the main content will be as wide as necessary to fill the screen. Additionally, this can then be combined with media queries to switch to an all-vertical layout on narrow screens:
<pre>
@media all and (max-width: 600px) {
/* Too narrow to support three columns */
#main { flex-flow: column; }
#main > article, #main > nav, #main > aside {
/* Return them to document order */
flex-order: 0; width: auto;
}
}</pre>
<p><small>(Further use of multiline flexboxes to achieve even more intelligent wrapping left as an exercise for the reader.)</small>
</div>
<h2 id='flexibility'>
Flexibility: the 'flex' property</h2>
<p>
The defining aspect of flexbox layout is the ability to make the <i>flexbox items</i> "flex",
altering their width or height to fill the available space.
This is done with the 'flex' property.
A flexbox distributes free space to its items proportional to their <i>positive flex ratio</i>,
or shrinks them to prevent overflow proportional to their <i>negative flex ratio</i>.
<table class=propdef>
<tr>
<th>Name:
<td><dfn>flex</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>none | [ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]
<tr>
<th>Initial:
<td>see individual properties
<tr>
<th>Applies to:
<td>flexbox items
<tr>
<th>Inherited:
<td>see individual properties
<tr>
<th>Computed Value:
<td>see individual properties
<tr>
<th>Media:
<td>visual
<tr>
<th>Animatable:
<td>see individual properties
<tr>
<th>Canonical Order:
<td>per grammar
</table>
<p>
The 'flex' property specifies the components of a <dfn title="flexible length|flexible length's">flexible length</dfn>:
the <dfn id="positive-flexibility" title="positive flex ratio">positive</dfn>
and <dfn>negative flex ratio</dfn>,
and the <dfn>flex basis</dfn>.
When an element is a <i>flexbox item</i>,
'flex' is consulted <em>instead of</em> the <i>main size property</i>
to determine the <i>main size</i> of the element.
If an element is not a <i>flexbox item</i>,
'flex' has no effect.
<p>
The <var><'flex-basis'></var> component sets the <i>flex basis</i>.
If omitted, the flex basis defaults to ''0px''.
<span class='note'>Note that this is different from the initial value of 'flex-basis'.</span>
<p>
If the <var><'flex-basis'></var> is zero,
it <strong>must</strong> be specified with a unit
(like ''0px'')
or omitted
to avoid ambiguity;
unitless zero will either be interpreted as as one of the flex ratios,
or will make the declaration invalid.
<p>
The keyword 'none' computes to ''0 0 auto''.
<div class='example'>
<p>
Flexibility allows elements to respond directly to the available space,
optionally taking into account size of content:
<pre>
<!DOCTYPE html>
<style>
div { display:flex; outline:1px solid silver; }
p { flex:1 auto; margin:1em; background:gold; }
</style>
<div>
<p>"flexing"</p>
<p>allows the items to get bigger</p>
<p>or</p>
<p>smaller</p>
</div>
</pre>
<p>
Here, all four paragraphs have a <i>flex basis</i> equal to the length of their text.
The leftover space
(after subtracting their flex basises and margins from the width of the flexbox)
is distributed evenly to the four paragraphs.
This shows how elements with the same flexibility may still end up different sizes,
if their flex basises are different.
<img src="images/wp7zxxyu.gif" alt="">
</div>
<h3 id='flex-components'>
Components of Flexibility: the 'flex-grow', 'flex-shrink' and 'flex-basis' properties</h3>
<p>
Individual components of flexibility can be controlled by separate properties.
<p class='note'>
Authors are encouraged to control flexibility using the 'flex' shorthand
rather than with component properties.
<table class=propdef>
<tr>
<th>Name:
<td><dfn>flex-grow</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><number>
<tr>
<th>Initial:
<td>''1''
<tr>
<th>Applies to:
<td>flexbox items
<tr>
<th>Inherited:
<td>no
<tr>
<th>Computed Value:
<td>specified value
<tr>
<th>Media:
<td>visual
<tr>
<th>Animatable:
<td>yes, except between ''0'' and other values
<tr>
<th>Canonical Order:
<td><abbr title="follows order of property value definition">per grammar</abbr>
</table>
<p>
The 'flex-grow' property sets the <i>positive flex ratio</i>.
Negative numbers are invalid.
<table class=propdef>
<tr>
<th>Name:
<td><dfn>flex-shrink</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><number>
<tr>
<th>Initial:
<td>''1''
<tr>
<th>Applies to:
<td>flexbox items
<tr>
<th>Inherited:
<td>no
<tr>
<th>Computed Value:
<td>specified value
<tr>
<th>Media:
<td>visual
<tr>
<th>Animatable:
<td>yes, except between ''0'' and other values
<tr>
<th>Canonical Order:
<td><abbr title="follows order of property value definition">per grammar</abbr>
</table>
<p>
The 'flex-shrink' property sets the <i>negative flex ratio</i>.
Negative numbers are invalid.
<table class=propdef>
<tr>
<th>Name:
<td><dfn>flex-basis</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><var><'width'></var>
<tr>
<th>Initial:
<td>auto
<tr>
<th>Applies to:
<td>flexbox items
<tr>
<th>Inherited:
<td>no
<tr>
<th>Computed Value:
<td>an absolute length, or a percentage or a keyword as specified
<tr>
<th>Media:
<td>visual
<tr>
<th>Animatable:
<td>yes, insofar as 'width' is animatable
<tr>
<th>Canonical Order:
<td><abbr title="follows order of property value definition">per grammar</abbr>
</table>
<p>
The 'flex-basis' property sets the <i>flex basis</i>.
Negative lengths are invalid.
<p>
If the <var><'width'></var> component is ''auto'' on a child of a <i>flexbox</i>,
the used <i>flex basis</i> is the computed value of the <i>main size property</i>.