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<!DOCTYPE html><html lang=en><head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Flexible Box Layout Module Level 1</title>
<link href=../default.css rel=stylesheet type=text/css>
<link href=../csslogo.ico rel="shortcut icon" type=image/x-icon>
<style>
body {
background: url("https://www.w3.org/StyleSheets/TR/logo-ED") top left no-repeat white;
background-attachment: fixed;
color: black;
font-family: sans-serif;
margin: 0 auto;
max-width: 50em;
padding: 2em 1em 2em 70px;
}
:link { color: #00C; background: transparent }
:visited { color: #609; background: transparent }
a[href]:active { color: #C00; background: transparent }
a[href]:hover { background: #ffa }
a[href] img { border-style: none }
h1, h2, h3, h4, h5, h6 { text-align: left }
h1, h2, h3 { color: #005A9C; }
h1 { font: 170% sans-serif }
h2 { font: 140% sans-serif }
h3 { font: 120% sans-serif }
h4 { font: bold 100% sans-serif }
h5 { font: italic 100% sans-serif }
h6 { font: small-caps 100% sans-serif }
.hide { display: none }
div.head { margin-bottom: 1em }
div.head h1 { margin-top: 2em; clear: both }
div.head table { margin-left: 2em; margin-top: 2em }
p.copyright { font-size: small }
p.copyright small { font-size: small }
pre { margin-left: 2em }
dt { font-weight: bold }
ul.toc, ol.toc {
list-style: none;
}
</style>
<script defer src=//test.csswg.org/harness/annotate.js#css-flexbox-1_dev/css-flexbox-1 type=text/javascript></script>
<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;
}
ol[start="0"] { counter-reset: list -1; }
ol[start="0"],
ol.continue { list-style: none; }
ol[start="0"] > li,
ol.continue > li { position: relative; counter-increment: list; }
ol[start="0"] > li::before,
ol.continue > li::before { content: counter(list) "."; position: absolute; left: -4.5em; width: 4em; text-align: right; }
.compact, .compact li {
margin-top: 0;
margin-bottom: 0;
}
/* Overview catalog example */
#overview-example {
display:table;
margin: 0 auto 1em;
border-spacing: .5em 0;
min-width: 672px;
}
#overview-example > .col {
display: table-column;
background: hsl(60,100%,90%);
}
#overview-example > .desc {
display: table-cell;
vertical-align: top;
width: 300px;
padding: 1em 1em 0;
text-align: left;
border: thick solid hsl(60,80%,50%);
border-radius: 1em 1em 0 0;
border-bottom: none;
}
#overview-example > .desc > img {
margin: 0 auto;
display: block;
}
#overview-example > .desc > h1 {
background: transparent;
}
#overview-example > .buttons {
display: table-row;
}
#overview-example > .buttons > div {
display: table-cell;
border: thick solid hsl(60,80%,50%);
border-radius: 0 0 1em 1em;
border-top: none;
text-align: center;
}
#overview-example button {
background-color: hsl(120,100%,40%);
border: medium inset hsl(120,70%,40%);
border-radius: 1em;
padding: .5em;
font-weight: bold;
color: white;
font-size: 1.6em;
cursor: pointer;
width: 90%;
margin: 1em auto;
}
/* Visibility: Collapse example */
#visibility-collapse-example {
display: table;
width: 100%;
box-shadow: 3px 3px 10px #333;
}
#visibility-collapse-example > article,
#visibility-collapse-example > nav {
display: table-cell;
}
#visibility-collapse-example > article {
width: 100%;
background: white;
}
#visibility-collapse-example ul,
#visibility-collapse-example li {
margin: 0;
padding: 0;
}
#visibility-collapse-example > nav > ul {
background: #444;
border-radius: 0.5em;
padding: 0.075em;
}
#visibility-collapse-example li {
padding: 0 0.5em;
background: #ddd;
color: black;
border-radius: 0.40em;
border: #444 solid 0.075em;
}
#visibility-collapse-example li li {
background: #444;
color: white;
margin: 0 -0.5em;
border-radius: 0;
}
#visibility-collapse-example li li:first-child {
border-radius: 0.375em 0.375em 0 0;
}
#visibility-collapse-example a {
background: transparent;
color: inherit;
}
#visibility-collapse-example > nav > ul > li:target,
#visibility-collapse-example > nav > ul > li:hover {
background: #888;
color: white;
}
#visibility-collapse-example > nav > ul > li:not(:target):not(:hover) > ul {
height: 0;
overflow: hidden;
}
#auto-bar {
overflow: hidden;
padding: .25em 1em;
background: #ddd;
list-style: none;
margin: 0;
border-radius: .3em;
}
#auto-bar > li {
float: left;
color: black;
margin: 0;
}
#auto-bar > li:first-child:after,
#auto-bar > li:first-child + li:after {
content: " | ";
white-space: pre;
}
#auto-bar > li > a {
display: inline-block;
padding: 0 .25em;
border-radius: .3em;
}
#auto-bar > li > a:not(:hover):not(:focus) {
text-decoration: none;
}
#auto-bar > li > a:hover {
color: #ddd;
background: #444;
}
#auto-bar > #login { float: right; }
.cross-auto-figure > div {
margin: 0 auto;
width: 70px;
background: #888;
padding: 0 .5em;
border-radius: 1em;
border: 1px solid transparent;
}
.cross-auto-figure > div > div {
border-spacing: 0;
display: table;
background: #ddd;
color: black;
text-align: center;
margin: .5em auto;
padding: .5em;
border-radius: .5em;
}
.axis { color: hsl( 0,80%,40%); }
.side { color: hsl(240,80%,50%); }
.size { color: hsl(120,80%,30%); }
</style>
</head>
<body class=h-entry>
<div class=head>
<p data-fill-with=logo><a class=logo href=http://www.w3.org/>
<img alt=W3C height=48 src=https://www.w3.org/Icons/w3c_home width=72>
</a>
</p>
<h1 class="p-name no-ref" id=title>CSS Flexible Box Layout Module Level 1</h1>
<h2 class="no-num no-toc no-ref heading settled" id=subtitle><span class=content>Editor’s Draft,
<span class=dt-updated><span class=value-title title=20141104>4 November 2014</span></span></span></h2>
<div data-fill-with=spec-metadata><dl><dt>This version:<dd><a class=u-url href=http://dev.w3.org/csswg/css-flexbox/>http://dev.w3.org/csswg/css-flexbox/</a><dt>Latest version:<dd><a href=http://www.w3.org/TR/css-flexbox-1/>http://www.w3.org/TR/css-flexbox-1/</a><dt>Previous Versions:<dd><a href=http://www.w3.org/TR/2014/WD-css-flexbox-1-20140325/ rel=previous>http://www.w3.org/TR/2014/WD-css-flexbox-1-20140325/</a><dd><a href=http://www.w3.org/TR/2012/CR-css3-flexbox-20120918/ rel=previous>http://www.w3.org/TR/2012/CR-css3-flexbox-20120918/</a><dd><a href=http://www.w3.org/TR/2012/WD-css3-flexbox-20120612/ rel=previous>http://www.w3.org/TR/2012/WD-css3-flexbox-20120612/</a><dd><a href=http://www.w3.org/TR/2012/WD-css3-flexbox-20120322/ rel=previous>http://www.w3.org/TR/2012/WD-css3-flexbox-20120322/</a><dd><a href=http://www.w3.org/TR/2011/WD-css3-flexbox-20111129/ rel=previous>http://www.w3.org/TR/2011/WD-css3-flexbox-20111129/</a><dd><a href=http://www.w3.org/TR/2011/WD-css3-flexbox-20110322/ rel=previous>http://www.w3.org/TR/2011/WD-css3-flexbox-20110322/</a><dd><a href=http://www.w3.org/TR/2009/WD-css3-flexbox-20090723/ rel=previous>http://www.w3.org/TR/2009/WD-css3-flexbox-20090723/</a><dt>Feedback:<dd><span><a href="mailto:www-style@w3.org?subject=[css-flexbox] feedback">www-style@w3.org</a> with subject line “<kbd>[css-flexbox] <var>… message topic …</var></kbd>” (<a href=http://lists.w3.org/Archives/Public/www-style/ rel=discussion>archives</a>)</span><dt>Test Suite:<dd><a href=http://test.csswg.org/suites/css-flexbox-1_dev/nightly-unstable/>http://test.csswg.org/suites/css-flexbox-1_dev/nightly-unstable/</a><dt>Editors:<dd><div class="p-author h-card vcard"><a class="p-name fn u-url url" href=http://xanthir.com/contact/>Tab Atkins Jr.</a> (<span class="p-org org">Google</span>)</div><dd><div class="p-author h-card vcard"><a class="p-name fn u-url url" href=http://fantasai.inkedblade.net/contact>fantasai</a> (<span class="p-org org">Mozilla</span>)</div><dd><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:ratan@microsoft.com>Rossen Atanassov</a> (<span class="p-org org">Microsoft</span>)</div><dt>Former Editors:<dd><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:alexmog@microsoft.com>Alex Mogilevsky</a> (<span class="p-org org">Microsoft Corporation</span>)</div><dd><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:dbaron@dbaron.org>L. David Baron</a> (<span class="p-org org">Mozilla Corporation</span>)</div><dd><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:enndeakin@gmail.com>Neil Deakin</a> (<span class="p-org org">Mozilla Corporation</span>)</div><dd><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:ian@hixie.ch>Ian Hickson</a> (<span class="p-org org">formerly of Opera Software</span>)</div><dd><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:hyatt@apple.com>David Hyatt</a> (<span class="p-org org">formerly of Netscape Corporation</span>)</div><dt>Issues List:<dd><span><a href=http://dev.w3.org/csswg/css-flexbox-1/issues-lc-20140925>http://dev.w3.org/csswg/css-flexbox-1/issues-lc-20140925</a></span></dl></div>
<div data-fill-with=warning></div>
<p class=copyright data-fill-with=copyright><a href=http://www.w3.org/Consortium/Legal/ipr-notice#Copyright>Copyright</a> © 2014 <a href=http://www.w3.org/><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href=http://www.csail.mit.edu/><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href=http://www.ercim.eu/><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href=http://www.keio.ac.jp/>Keio</a>, <a href=http://ev.buaa.edu.cn/>Beihang</a>), All Rights Reserved. W3C <a href=http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer>liability</a>, <a href=http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks>trademark</a> and <a href=http://www.w3.org/Consortium/Legal/copyright-documents>document use</a> rules apply.
</p>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled" id=abstract><span class=content>Abstract</span></h2>
<div class=p-summary data-fill-with=abstract><p>The specification describes a CSS box model optimized for user interface design. In the flex layout model, the children of a flex container 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.</p>
<a href=http://www.w3.org/TR/CSS/>CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.</div>
<h2 class="no-num no-toc no-ref heading settled" id=status><span class=content>Status of this document</span></h2>
<div data-fill-with=status><p>
This is a public copy of the editors’ draft.
It is provided for discussion only and may change at any moment.
Its publication here does not imply endorsement of its contents by W3C.
Don’t cite this document other than as work in progress.
<p>
The (<a href=http://lists.w3.org/Archives/Public/www-style/>archived</a>) public mailing list
<a href="mailto:www-style@w3.org?Subject=%5Bcss-flexbox%5D%20PUT%20SUBJECT%20HERE">www-style@w3.org</a>
(see <a href=http://www.w3.org/Mail/Request>instructions</a>)
is preferred for discussion of this specification.
When sending e-mail,
please put the text “css-flexbox” in the subject,
preferably like this:
“[css-flexbox] <em>…summary of comment…</em>”
<p>
This document was produced by the <a href=http://www.w3.org/Style/CSS/members>CSS Working Group</a>
(part of the <a href=http://www.w3.org/Style/>Style Activity</a>).
<p>
This document was produced by a group operating under
the <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/>5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href=http://www.w3.org/2004/01/pp-impl/32061/status rel=disclosure>public list of any patent disclosures</a>
made in connection with the deliverables of the group;
that page also includes instructions for disclosing a patent.
An individual who has actual knowledge of a patent which the individual believes contains <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential>Essential Claim(s)</a>
must disclose the information in accordance with <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure>section 6 of the W3C Patent Policy</a>.
<p>
This document is governed by the <a href=http://www.w3.org/2014/Process-20140801/>1 August 2014 W3C Process Document</a>.
</div>
<div data-fill-with=at-risk></div>
<h2 class="no-num no-toc no-ref heading settled" id=contents><span class=content>Table of Contents</span></h2>
<div data-fill-with=table-of-contents><ul class=toc><li><a href=#intro><span class=secno>1</span> <span class=content>
Introduction</span></a><ul class=toc><li><a href=#overview><span class=secno>1.1</span> <span class=content>
Overview</span></a><li><a href=#placement><span class=secno>1.2</span> <span class=content>
Module interactions</span></a><li><a href=#values><span class=secno>1.3</span> <span class=content>
Values</span></a></ul><li><a href=#box-model><span class=secno>2</span> <span class=content>
Flex Layout Box Model and Terminology</span></a><li><a href=#flex-containers><span class=secno>3</span> <span class=content>
Flex Containers: the <span class=css data-link-type=maybe title=flex>flex</span> and <span class=css data-link-type=maybe title=inline-flex>inline-flex</span> <span class=property data-link-type=propdesc title=display>display</span> values</span></a><li><a href=#flex-items><span class=secno>4</span> <span class=content>
Flex Items</span></a><ul class=toc><li><a href=#abspos-items><span class=secno>4.1</span> <span class=content>
Absolutely-Positioned Flex Children</span></a><li><a href=#item-margins><span class=secno>4.2</span> <span class=content>
Flex Item Margins and Paddings</span></a><li><a href=#painting><span class=secno>4.3</span> <span class=content>
Flex Item Z-Ordering</span></a><li><a href=#visibility-collapse><span class=secno>4.4</span> <span class=content>
Collapsed Items</span></a><li><a href=#min-size-auto><span class=secno>4.5</span> <span class=content>
Implied Minimum Size of Flex Items</span></a></ul><li><a href=#flow-order><span class=secno>5</span> <span class=content>
Ordering and Orientation</span></a><ul class=toc><li><a href=#flex-direction-property><span class=secno>5.1</span> <span class=content>
Flex Flow Direction: the <span class=property data-link-type=propdesc title=flex-direction>flex-direction</span> property</span></a><li><a href=#flex-wrap-property><span class=secno>5.2</span> <span class=content>
Flex Line Wrapping: the <span class=property data-link-type=propdesc title=flex-wrap>flex-wrap</span> property</span></a><li><a href=#flex-flow-property><span class=secno>5.3</span> <span class=content>
Flex Direction and Wrap: the <span class=property data-link-type=propdesc title=flex-flow>flex-flow</span> shorthand</span></a><li><a href=#order-property><span class=secno>5.4</span> <span class=content>
Display Order: the <span class=property data-link-type=propdesc title=order>order</span> property</span></a><ul class=toc><li><a href=#order-accessibility><span class=secno>5.4.1</span> <span class=content>
Reordering and Accessibility</span></a></ul></ul><li><a href=#flex-lines><span class=secno>6</span> <span class=content>
Flex Lines</span></a><li><a href=#flexibility><span class=secno>7</span> <span class=content>
Flexibility</span></a><ul class=toc><li><a href=#flex-property><span class=secno>7.1</span> <span class=content>
The <span class=property data-link-type=propdesc title=flex>flex</span> Shorthand</span></a><li><a href=#flex-common><span class=secno>7.2</span> <span class=content>
Common Values of <span class=property data-link-type=propdesc title=flex>flex</span></span></a><li><a href=#flex-components><span class=secno>7.3</span> <span class=content>
Components of Flexibility</span></a><ul class=toc><li><a href=#flex-grow-property><span class=secno>7.3.1</span> <span class=content>
The <span class=property data-link-type=propdesc title=flex-grow>flex-grow</span> property</span></a><li><a href=#flex-shrink-property><span class=secno>7.3.2</span> <span class=content>
The <span class=property data-link-type=propdesc title=flex-shrink>flex-shrink</span> property</span></a><li><a href=#flex-basis-property><span class=secno>7.3.3</span> <span class=content>
The <span class=property data-link-type=propdesc title=flex-basis>flex-basis</span> property</span></a></ul></ul><li><a href=#alignment><span class=secno>8</span> <span class=content>
Alignment</span></a><ul class=toc><li><a href=#auto-margins><span class=secno>8.1</span> <span class=content>
Aligning with <span data-link-for=margin data-link-type=value title=auto>auto</span> margins</span></a><li><a href=#justify-content-property><span class=secno>8.2</span> <span class=content>
Axis Alignment: the <span class=property data-link-type=propdesc title=justify-content>justify-content</span> property</span></a><li><a href=#align-items-property><span class=secno>8.3</span> <span class=content>
Cross-axis Alignment: the <span class=property data-link-type=propdesc title=align-items>align-items</span> and <span class=property data-link-type=propdesc title=align-self>align-self</span> properties</span></a><li><a href=#align-content-property><span class=secno>8.4</span> <span class=content>
Packing Flex Lines: the <span class=property data-link-type=propdesc title=align-content>align-content</span> property</span></a><li><a href=#flex-baselines><span class=secno>8.5</span> <span class=content>
Flex Baselines</span></a></ul><li><a href=#layout-algorithm><span class=secno>9</span> <span class=content>
Flex Layout Algorithm</span></a><ul class=toc><li><a href=#box-manip><span class=secno>9.1</span> <span class=content>
Initial Setup</span></a><li><a href=#line-sizing><span class=secno>9.2</span> <span class=content>
Line Length Determination</span></a><li><a href=#main-sizing><span class=secno>9.3</span> <span class=content>
Main Size Determination</span></a><li><a href=#cross-sizing><span class=secno>9.4</span> <span class=content>
Cross Size Determination</span></a><li><a href=#main-alignment><span class=secno>9.5</span> <span class=content>
Main-Axis Alignment</span></a><li><a href=#cross-alignment><span class=secno>9.6</span> <span class=content>
Cross-Axis Alignment</span></a><li><a href=#resolve-flexible-lengths><span class=secno>9.7</span> <span class=content>
Resolving Flexible Lengths</span></a><li><a href=#definite-sizes><span class=secno>9.8</span> <span class=content>
Definite and Indefinite Sizes</span></a><li><a href=#intrinsic-sizes><span class=secno>9.9</span> <span class=content>
Intrinsic Sizes</span></a></ul><li><a href=#pagination><span class=secno>10</span> <span class=content>
Fragmenting Flex Layout</span></a><ul class=toc><li><a href=#pagination-algo><span class=secno>10.1</span> <span class=content>
Sample Flex Fragmentation Algorithm</span></a></ul><li><a href=#acknowledgments><span class=secno></span> <span class=content>Acknowledgments</span></a><li><a href=#changes><span class=secno></span> <span class=content>Changes</span></a><ul class=toc><li><a href=#changes-201403><span class=secno></span> <span class=content>
Changes since the 25 March 2014 LCWD</span></a><ul class=toc><li><a href=#change-201403-substantive><span class=secno></span> <span class=content>
Substantive Changes and Bugfixes</span></a><li><a href=#change-201403-clarify><span class=secno></span> <span class=content>
Clarifications</span></a></ul><li><a href=#changes-2012><span class=secno></span> <span class=content>
Changes since the 18 September 2012 Candidate Recommendation</span></a><ul class=toc><li><a href=#changes-2014-substantive><span class=secno></span> <span class=content>
Substantive Changes and Bugfixes</span></a><li><a href=#changes-2014-clarify><span class=secno></span> <span class=content>
Clarifications</span></a></ul></ul><li><a href=#conformance><span class=secno></span> <span class=content>
Conformance</span></a><ul class=toc><li><a href=#conventions><span class=secno></span> <span class=content>
Document conventions</span></a><li><a href=#conformance-classes><span class=secno></span> <span class=content>
Conformance classes</span></a><li><a href=#partial><span class=secno></span> <span class=content>
Partial implementations</span></a><li><a href=#experimental><span class=secno></span> <span class=content>
Experimental implementations</span></a><li><a href=#testing><span class=secno></span> <span class=content>
Non-experimental implementations</span></a></ul><li><a href=#references><span class=secno></span> <span class=content>References</span></a><ul class=toc><li><a href=#normative><span class=secno></span> <span class=content>Normative References</span></a><li><a href=#informative><span class=secno></span> <span class=content>Informative References</span></a></ul><li><a href=#index><span class=secno></span> <span class=content>Index</span></a><li><a href=#property-index><span class=secno></span> <span class=content>Property Index</span></a><li><a href=#issues-index><span class=secno></span> <span class=content>Issues Index</span></a></ul></div>
<h2 class="heading settled" data-level=1 id=intro><span class=secno>1. </span><span class=content>
Introduction</span><a class=self-link href=#intro></a></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:
<ul class=compact>
<li>block layout, designed for laying out documents
<li>inline layout, designed for laying out text
<li>table layout, designed for laying out 2D data in a tabular format
<li>positioned layout, designed for very explicit positioning without much regard for other elements in the document
</ul>
<p>
This module introduces a new layout mode, <dfn data-dfn-type=dfn data-export="" id=flex-layout>flex layout<a class=self-link href=#flex-layout></a></dfn>,
which is designed for laying out more complex applications and webpages.
<h3 class="heading settled" data-level=1.1 id=overview><span class=secno>1.1. </span><span class=content>
Overview</span><a class=self-link href=#overview></a></h3>
<p><em>This section is not normative.</em>
<p>
Flex layout is superficially similar to block layout.
It lacks many of the more complex text- or document-centric properties
that can be used in block layout, such as
<a href=http://www.w3.org/TR/CSS21/visuren.html#floats>floats</a> and
<a href=http://www.w3.org/TR/css3-multicol/>columns</a>.
In return it gains simple and powerful tools
for distributing space and aligning content
in ways that webapps and complex web pages often need.
The contents of a flex container:
<ul>
<li>
can be laid out in any <a href=#flex-direction-property>flow direction</a>
(leftwards, rightwards, downwards, or even upwards!)
<li>
can have their display order <a class=css data-link-for=flex-direction data-link-type=value href=#valdef-flex-direction-row-reverse title=row-reverse>reversed</a> or
<a href=#order-property>rearranged</a> at the style layer
(i.e., visual order can be independent of source and speech order)
<li>
can be laid out linearly along a single (<a data-link-type=dfn href=#main-axis title="main axis">main</a>) axis or
<a href=#flex-wrap-property>wrapped</a> into multiple lines along a secondary (<a data-link-type=dfn href=#cross-axis title="cross axis">cross</a>) axis
<li>
can <a href=#flexibility>“flex” their sizes</a>
to respond to the available space
<li>
can be <a href=#alignment>aligned</a> with respect to their container or each other
<li>
can be dynamically <a href=#visibility-collapse>collapsed</a> or uncollapsed
along the <a data-link-type=dfn href=#main-axis title="main axis">main axis</a> while preserving the container’s <a data-link-type=dfn href=#cross-size title="cross size">cross size</a>
</ul>
<div class=example>
<p>
Here’s an example of a catalog where each item has a title, an photo, a description, and a purchase button.
The designer’s intention is that each entry has the same overall size,
that the photo be above the text,
and that the purchase buttons aligned at the bottom, regardless of the length of the item’s description.
Flex layout makes many aspects of this design easy:
<ul>
<li>
The catalog uses flex layout to lay out rows of items horizontally,
and to ensure that items within a row are all equal-height.
Each entry is then itself a column flex container,
laying out its contents vertically.
<li>
Within each entry, the source document content is ordered logically
with the title first, followed by the description and the photo.
This provides a sensible ordering for speech rendering and in non-CSS browsers.
For a more compelling visual presentation, however,
<a class=property data-link-type=propdesc href=#propdef-order title=order>order</a> is used to pull the image up from later in the content to the top,
and <a class=property data-link-type=propdesc href=#propdef-align-self title=align-self>align-self</a> is used to center it horizontally.
<li>
An <a href=#auto-margins><span class=css>auto</span> margin</a> above the purchase button
forces it to the bottom within each entry box,
regardless of the height of that item’s description.
</ul>
<pre><style>
#deals {
display: flex; /* Flex layout so items <a data-link-type=property href=#propdef-align-self title=align-self>have equal height</a> */
flex-flow: row wrap; /* <a data-section="" href=#flex-flow-property>Allow items to wrap into multiple lines</a> */
}
.sale-item {
display: flex; /* Lay out each item using flex layout */
flex-flow: column; /* <a data-section="" href=#flex-flow-property>Lay out item’s contents vertically</a> */
}
.sale-item > img {
order: -1; /* <a data-section="" href=#order-property>Shift image before other content (in visual order)</a> */
align-self: center; /* <a data-link-type=property href=#propdef-align-self title=align-self>Center the image cross-wise (horizontally)</a> */
}
.sale-item > button {
margin-top: auto; /* <a data-section="" href=#auto-margins>Auto top margin pushes button to bottom</a> */
}
</style></pre>
<pre><section id='deals'>
<section class='sale-item'>
<h1>Computer Starter Kit</h1>
<p>This is the best computer money can buy, if you don’t have much money.
<ul>
<li>Computer
<li>Monitor
<li>Keyboard
<li>Mouse
</ul>
<img src='images/computer.jpg'
alt='You get: a white computer with matching peripherals.'>
<button>BUY NOW</button>
</section>
<section class='sale-item'>
…
</section>
…
</section></pre>
<figure>
<div id=overview-example>
<div class=col></div>
<div class=col></div>
<div class=desc>
<img alt="You get: a white computer with matching keyboard and monitor." src=images/computer.jpg>
<h1 id=quiet-pubrules-1 style="font-size: 1.4em;">Computer Starter Kit</h1>
<p>
This is the best computer money can buy,
if you don’t have much money.
<ul>
<li>Computer
<li>Monitor
<li>Keyboard
<li>Mouse
</ul>
</div>
<div class=desc>
<img alt="You get: beautiful ASCII art." src=images/printer.png>
<h1 id=quiet-pubrules-2 style="font-size: 1.4em;">Printer</h1>
<p>
Only capable of printing
ASCII art.
<ul>
<li>Paper and ink not included.
</ul>
</div>
<div class=buttons>
<div><button>BUY NOW</button></div>
<div><button>BUY NOW</button></div>
</div>
</div>
<figcaption>
An example rendering of the code above.
</figcaption>
</figure>
</div>
<h3 class="heading settled" data-level=1.2 id=placement><span class=secno>1.2. </span><span class=content>
Module interactions</span><a class=self-link href=#placement></a></h3>
<p>
This module extends the definition of the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> property <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>,
adding a new block-level and new inline-level display type,
and defining a new type of formatting context
along with properties to control its layout.
None of the properties defined in this module apply to the <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-pseudo-4/#selectordef-first-line title=::first-line>::first-line</a> or <span class=css>::first-letter</span> pseudo-elements.
<h3 class="heading settled" data-level=1.3 id=values><span class=secno>1.3. </span><span class=content>
Values</span><a class=self-link href=#values></a></h3>
<p>
This specification follows the <a href=http://www.w3.org/TR/CSS21/about.html#property-defs>CSS property definition conventions</a> from <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>.
Value types not defined in this specification are defined in CSS Level 2 Revision 1 <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>.
Other CSS modules may expand the definitions of these value types:
for example <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3val title=CSS3VAL>[CSS3VAL]</a>, when combined with this module,
expands the definition of the <var><length></var> 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 <span class=css>inherit</span> keyword as their property value. For readability it has not been repeated explicitly.
<h2 class="heading settled" data-level=2 id=box-model><span class=secno>2. </span><span class=content>
Flex Layout Box Model and Terminology</span><a class=self-link href=#box-model></a></h2>
<p>
A <dfn data-dfn-type=dfn data-export="" id=flex-container>flex container<a class=self-link href=#flex-container></a></dfn> is the box generated by an element with a
computed <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> of <a class=css data-link-type=maybe href=#valdef-display-flex title=flex>flex</a> or <a class=css data-link-type=maybe href=#valdef-display-inline-flex title=inline-flex>inline-flex</a>.
In-flow children of a flex container are called <dfn data-dfn-type=dfn data-export="" id=flex-item title="flex item">flex items<a class=self-link href=#flex-item></a></dfn>
and are laid out using the flex layout model.
<p>
Unlike block and inline layout,
whose layout calculations are biased to the <a href=http://www.w3.org/TR/css3-writing-modes/#abstract-box>block and inline flow directions</a>,
flex layout is biased to the <dfn data-dfn-type=dfn data-noexport="" id=flex-direction title="flex direction">flex directions<a class=self-link href=#flex-direction></a></dfn>.
To make it easier to talk about flex layout,
this section defines a set of flex flow–relative terms.
The <a class=property data-link-type=propdesc href=#propdef-flex-flow title=flex-flow>flex-flow</a> value determines how these terms map
to physical directions (top/right/bottom/left),
axes (vertical/horizontal), and sizes (width/height).
</p><figure>
<img alt="" height=277 src=images/flex-direction-terms.svg width=665>
<figcaption>
An illustration of the various directions and sizing terms as applied to a <a class=css data-link-type=maybe href=#valdef-flex-direction-row title=row>row</a> flex container.
</figcaption>
</figure>
<dl data-export="" id=main>
<dt class=axis>main axis
<dt class=axis>main dimension
<dd>
The <dfn data-dfn-type=dfn data-export="" id=main-axis title="main axis|main-axis">main axis<a class=self-link href=#main-axis></a></dfn> of a flex container is the primary axis along which <a data-link-type=dfn href=#flex-item title="flex items">flex items</a> are laid out.
It extends in the <dfn data-dfn-type=dfn data-export="" id=main-dimension>main dimension<a class=self-link href=#main-dimension></a></dfn>.
<dt class=side>main-start
<dt class=side>main-end
<dd>
The <a data-link-type=dfn href=#flex-item title="flex items">flex items</a> are placed within the container
starting on the <dfn data-dfn-type=dfn data-export="" id=main-start>main-start<a class=self-link href=#main-start></a></dfn> side
and going toward the <dfn data-dfn-type=dfn data-export="" id=main-end>main-end<a class=self-link href=#main-end></a></dfn> side.
<dt class=size>main size
<dt class=size>main size property
<dd>
A <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>’s width or height,
whichever is in the <a data-link-type=dfn href=#main-dimension title="main dimension">main dimension</a>,
is the item’s <dfn data-dfn-type=dfn data-export="" id=main-size>main size<a class=self-link href=#main-size></a></dfn>.
The <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>’s <dfn data-dfn-type=dfn data-export="" id=main-size-property title="main size property|max main size property|min main size property">main size property<a class=self-link href=#main-size-property></a></dfn> is
either the <a class=property data-link-type=propdesc href=http://dev.w3.org/
8348
csswg/css2/visudet.html#propdef-width title=width>width</a> or <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-height title=height>height</a> property,
whichever is in the <a data-link-type=dfn href=#main-dimension title="main dimension">main dimension</a>.
</dl>
<dl data-export="" id=cross>
<dt class=axis>cross axis
<dt class=axis>cross dimension
<dd>
The axis perpendicular to the <a data-link-type=dfn href=#main-axis title="main axis">main axis</a> is called the <dfn data-dfn-type=dfn data-export="" id=cross-axis title="cross axis|cross-axis">cross axis<a class=self-link href=#cross-axis></a></dfn>.
It extends in the <dfn data-dfn-type=dfn data-export="" id=cross-dimension>cross dimension<a class=self-link href=#cross-dimension></a></dfn>.
<dt class=side>cross-start
<dt class=side>cross-end
<dd>
<a data-link-type=dfn href=#flex-line title="Flex lines">Flex lines</a> are filled with items and placed into the container
starting on the <dfn data-dfn-type=dfn data-export="" id=cross-start>cross-start<a class=self-link href=#cross-start></a></dfn> side of the flex container
and going toward the <dfn data-dfn-type=dfn data-export="" id=cross-end>cross-end<a class=self-link href=#cross-end></a></dfn> side.
<dt class=size>cross size
<dt class=size>cross size property
<dd>
The width or height of a <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>,
whichever is in the <a data-link-type=dfn href=#cross-dimension title="cross dimension">cross dimension</a>,
is the item’s <dfn data-dfn-type=dfn data-export="" id=cross-size>cross size<a class=self-link href=#cross-size></a></dfn>.
The <dfn data-dfn-type=dfn data-export="" id=cross-size-property title="cross size property|max cross size property|min cross size property">cross size property<a class=self-link href=#cross-size-property></a></dfn> is
whichever of <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-width title=width>width</a> or <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-height title=height>height</a> that is in the <a data-link-type=dfn href=#cross-dimension title="cross dimension">cross dimension</a>.
</dl>
<h2 class="heading settled" data-level=3 id=flex-containers><span class=secno>3. </span><span class=content>
Flex Containers: the <a class=css data-link-type=maybe href=#valdef-display-flex title=flex>flex</a> and <a class=css data-link-type=maybe href=#valdef-display-inline-flex title=inline-flex>inline-flex</a> <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> values</span><a class=self-link href=#flex-containers></a></h2>
<table class="definition propdef partial"><tr><th>Name:<td><a class=css data-link-type=property href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a><tr><th>New values:<td class=prod>flex <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> inline-flex</table>
<dl data-dfn-for=display data-dfn-type=value>
<dt><dfn class=css data-dfn-for=display data-dfn-type=value data-export="" id=valdef-display-flex>flex<a class=self-link href=#valdef-display-flex></a></dfn>
<dd>
This value causes an element to generate a block-level <a data-link-type=dfn href=#flex-container title="flex container">flex container</a> box.
<dt><dfn class=css data-dfn-for=display data-dfn-type=value data-export="" id=valdef-display-inline-flex>inline-flex<a class=self-link href=#valdef-display-inline-flex></a></dfn>
<dd>
This value causes an element to generate an inline-level <a data-link-type=dfn href=#flex-container title="flex container">flex container</a> box.
</dl>
<p>
A <a data-link-type=dfn href=#flex-container title="flex container">flex container</a> establishes a new <dfn data-dfn-type=dfn data-export="" id=flex-formatting-context>flex formatting context<a class=self-link href=#flex-formatting-context></a></dfn> for its contents.
This is the same as establishing a block formatting context,
except that flex layout is used instead of block layout:
floats do not intrude into the flex container,
and the flex container’s margins do not collapse with the margins of its contents.
<a data-link-type=dfn href=#flex-container title="Flex containers">Flex containers</a> form a containing block for their contents
<a href=http://www.w3.org/TR/CSS21/visudet.html#containing-block-details>exactly like block containers do</a>. <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>
The <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-overflow-3/#overflow0 title=overflow>overflow</a> property applies to <a data-link-type=dfn href=#flex-container title="flex containers">flex containers</a>.
<p>
Flex containers are not block containers,
and so some properties that were designed with the assumption of block layout don’t apply in the context of flex layout.
In particular:
<ul>
<li>
all of the <a class=property data-link-type=propdesc title=column-*>column-*</a> properties in the Multicol module have no effect on a flex container.
<li>
<a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-float title=float>float</a> and <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-clear title=clear>clear</a> have no effect on a <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>,
and do not take it out-of-flow.
However, the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-float title=float>float</a> property can still affect box generation
by influencing the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> property’s computed value.
<li>
<a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-vertical-align title=vertical-align>vertical-align</a> has no effect on a flex item.
<li>
the <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-pseudo-4/#selectordef-first-line title=::first-line>::first-line</a> and <span class=css>::first-letter</span> pseudo-elements do not apply to <a data-link-type=dfn href=#flex-container title="flex containers">flex containers</a>,
and <a data-link-type=dfn href=#flex-container title="flex containers">flex containers</a> do not contribute a <a data-link-type=dfn title="first formatted line">first formatted line</a> or <a data-link-type=dfn title="first letter">first letter</a>
to their ancestors.
</ul>
<p>
If an element’s specified <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> is <a class=css data-link-type=maybe href=#valdef-display-inline-flex title=inline-flex>inline-flex</a>,
then its <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> property computes to <a class=css data-link-type=maybe href=#valdef-display-flex title=flex>flex</a>
in certain circumstances:
the table in <a href=http://www.w3.org/TR/CSS2/visuren.html#dis-pos-flo>CSS 2.1 Section 9.7</a>
is amended to contain an additional row,
with <a class=css data-link-type=maybe href=#valdef-display-inline-flex title=inline-flex>inline-flex</a> in the "Specified Value" column
and <a class=css data-link-type=maybe href=#valdef-display-flex title=flex>flex</a> in the "Computed Value" column.
<h2 class="heading settled" data-level=4 id=flex-items><span class=secno>4. </span><span class=content>
Flex Items</span><a class=self-link href=#flex-items></a></h2>
<p>Loosely speaking, the <a data-link-type=dfn href=#flex-item title="flex items">flex items</a> of a <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>
are boxes representing its in-flow contents.
Each in-flow child of a <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>
becomes a <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>,
and each contiguous run of text that is directly contained inside a <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>
is wrapped in an anonymous <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>.
However, an anonymous flex item that contains only
<a href=http://www.w3.org/TR/CSS21/text.html#white-space-prop>white space</a>
(i.e. characters that can be affected by the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-text-3/#propdef-white-space title=white-space>white-space</a> property)
is not rendered, as if it were <span class=css>display:none</span>.</p>
<div class=example>
<p>Examples of flex items:
<pre><div style="display:flex">
<!-- flex item: block child -->
<div id="item1">block</div>
<!-- flex item: floated element; floating is ignored -->
<div id="item2" style="float: left;">float</div>
<!-- flex item: anonymous block box around inline content -->
anonymous item 3
<!-- flex item: inline child -->
<span>
item 4
<!-- flex items do not split around blocks -->
<div id=not-an-item>item 4</div>
item 4
</span>
</div></pre>
</div>
<p>
A <a data-link-type=dfn href=#flex-item title="flex item">flex item</a> establishes a new formatting context for its contents.
The type of this formatting context is determined by its <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> value, as usual.
However, flex items themselves are flex-level boxes, not block-level boxes:
they participate in their container’s flex formatting context,
not in a block formatting context.
<hr>
<p class=note>
Authors reading this spec may want to
<a href=#item-margins>skip past the following box-generation details</a>.
<p>The <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> value of a <a data-link-type=dfn href=#flex-item title="flex item">flex item</a> is <a data-link-type=dfn href=http://dev.w3.org/csswg/css-display-3/#blockify title=blockify>blockified</a>:
if the specified <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> of an in-flow child of an element generating a <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>
is an inline-level value, it computes to its block-level equivalent.
(See <a href=http://www.w3.org/TR/CSS21/visuren.html#dis-pos-flo>CSS2.1§9.7</a> <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>
and <a href=http://www.w3.org/TR/css-display/#transformations>CSS Display</a> <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3-display title=CSS3-DISPLAY>[CSS3-DISPLAY]</a>
for details on this type of <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> value conversion.)</p>
<p>Some values of <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display</a> trigger the creation of anonymous boxes around the original box.
It’s the outermost box—the direct child of the <a data-link-type=dfn href=#flex-container title="flex container">flex container</a> box—that
becomes a <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>.
For example, given two contiguous child elements with <a class=css data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display: table-cell</a>,
the <a href=http://www.w3.org/TR/CSS21/tables.html#anonymous-boxes>anonymous table wrapper box generated around them</a> <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>
becomes the <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>.</p>
<p id=table-items>
In the case of flex items with <a class=css data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display title=display>display: table</a>,
the table wrapper box becomes the <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>,
and the <a class=property data-link-type=propdesc href=#propdef-order title=order>order</a> and <a class=property data-link-type=propdesc href=#propdef-align-self title=align-self>align-self</a> properties apply to it.
The contents of any caption boxes contribute to the calculation of
the table wrapper box’s min-content and max-content sizes.
However, like <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-width title=width>width</a> and <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-height title=height>height</a>, the <a class=property data-link-type=propdesc href=#propdef-flex title=flex>flex</a> longhands apply to the table box as follows:
the <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>’s final size is calculated
by performing layout as if the distance between
the table wrapper box’s edges and the table box’s content edges
were all part of the table box’s border+padding area,
and the table box were the <a data-link-type=dfn href=#flex-item title="flex item">flex item</a>.
<h3 class="heading settled" data-level=4.1 id=abspos-items><span class=secno>4.1. </span><span class=content>
Absolutely-Positioned Flex Children</span><a class=self-link href=#abspos-items></a></h3>
<p>An absolutely-positioned child of a <a data-link-type=dfn href=#flex-container title="flex container">flex container</a> does not participate in flex layout.
However, it does participate in the <a href=#algo-flex-order>reordering step</a> (see <a class=property data-link-type=propdesc href=#propdef-order title=order>order</a>),
which has an effect in their painting order.</p>
<p>The <a href=http://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width>static position</a>
of an absolutely-positioned child of a <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>
is determined such that the child is positioned
as if it were the sole <a data-link-type=dfn href=#flex-item title="flex item">flex item</a> in the <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>,
assuming both the child and the flex container
were fixed-size boxes of their used size.</p>
<hr>
<p>In other words,
the <a data-link-type=dfn title="static position">static position</a> of an absolutely positioned child of a <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>
is determined <em>after flex layout</em>
by setting the child’s <a data-link-type=dfn href=#static-position-rectangle title="static-position rectangle">static-position rectangle</a> to the <a data-link-type=dfn href=#flex-container title="flex container’s">flex container’s</a> content box,
then aligning the absolutely positioned child within this rectangle
according to the <a class=property data-link-type=propdesc href=#propdef-justify-content title=justify-content>justify-content</a> value of the <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>
and the <a class=property data-link-type=propdesc href=#propdef-align-self title=align-self>align-self</a> value of the child itself.</p>
<div class=example>
The effect of this is that if you set, for example,
<a class=css data-link-type=propdesc href=#propdef-align-content title=align-content>align-content: center;</a> on an absolutely-positioned child of a <a data-link-type=dfn href=#flex-container title="flex container">flex container</a>,
the child’s static position will center it in the <a data-link-type=dfn href=#flex-container title="flex container’s">flex container’s</a> <a data-link-type=dfn href=#cross-axis title="cross axis">cross axis</a>.
</div>
<div class=note>
The <dfn data-dfn-type=dfn data-noexport="" id=static-position-rectangle>static-position rectangle<a class=self-link href=#static-position-rectangle></a></dfn> is the <a data-link-type=dfn href=http://dev.w3.org/csswg/css-align-3/#alignment-container title="alignment container">alignment container</a>
used to determine the static-position offsets of an absolutely-positioned box.
In block layout it corresponds to the position of the “hypothetical box”
described in <a href=http://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width>CSS2.1§10.3.7</a>.
(Since it has no alignment properties,
CSS2.1 always uses a <a data-link-type=dfn href=http://dev.w3.org/csswg/css-writing-modes-3/#block-start title=block-start>block-start</a> <a data-link-type=dfn href=http://dev.w3.org/csswg/css-writing-modes-3/#inline-start title=inline-start>inline-start</a> alignment
of the absolutely-positioned box within the <a data-link-type=dfn href=#static-position-rectangle title="static-position rectangle">static-position rectangle</a>.)
Note that this definition will eventually move to the CSS Positioning module.
</div>
<h3 class="heading settled" data-level=4.2 id=item-margins><span class=secno>4.2. </span><span class=content>
Flex Item Margins and Paddings</span><a class=self-link href=#item-margins></a></h3>
<p>
The margins of adjacent <a data-link-type=dfn href=#flex-item title="flex items">flex items</a> do not collapse.
Auto margins absorb extra space in the corresponding dimension and can be used for alignment
and to push adjacent flex items apart;
see <a href=#auto-margins>Aligning with <span class=css>auto</span> margins</a>.
<p>
Percentage margins and paddings on <a data-link-type=dfn href=#flex-item title="flex items">flex items</a> are always resolved against their respective dimensions;
unlike blocks, they do not always resolve against the inline dimension of their containing block.
<h3 class="heading settled" data-level=4.3 id=painting><span class=secno>4.3. </span><span class=content>
Flex Item Z-Ordering</span><a class=self-link href=#painting></a></h3>
<p>
<a data-link-type=dfn href=#flex-item title="Flex items">Flex items</a> paint exactly the same as inline blocks <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>,
except that <a class=property data-link-type=propdesc href=#propdef-order title=order>order</a>-modified document order is used in place of raw document order,
and <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-position-3/#propdef-z-index title=z-index>z-index</a>
values other than <span class=css data-link-for=z-index>auto</span> create a stacking context
even if <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-position-3/#propdef-position title=position>position</a> is <span class=css>static</span>.
<p class=note>
Note: Descendants that are positioned outside a flex item still participate
in any stacking context established by the flex item.
<h3 class="heading settled" data-level=4.4 id=visibility-collapse><span class=secno>4.4. </span><span class=content>
Collapsed Items</span><a class=self-link href=#visibility-collapse></a></h3>
<p>
Specifying <span class=css>visibility:collapse</span> on a flex item
causes it to become a <dfn data-dfn-type=dfn data-noexport="" id=collapsed-flex-item title="collapsed flex item|collapsed">collapsed flex item<a class=self-link href=#collapsed-flex-item></a></dfn>,
producing an effect similar to <span class=css>visibility:collapse</span> on a table-row or table-column:
the collapsed flex item is removed from rendering entirely,
but leaves behind a "strut" that keeps the flex line’s cross-size stable.
Thus, if a flex container has only one flex line,
dynamically collapsing or uncollapsing items
is guaranteed to have no effect on the flex container’s <a data-link-type=dfn href=#cross-size title="cross size">cross size</a>
and won’t cause the rest of the page’s layout to "wobble".
Flex line wrapping <em>is</em> re-done after collapsing, however,
so the cross-size of a flex container with multiple lines might or might not change.
<p>
Though collapsed flex items aren’t rendered,
they do appear in the <a href=http://www.w3.org/TR/CSS21/intro.html#formatting-structure>formatting structure</a>.
Therefore, unlike on <span class=css>display:none</span> items <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>,
effects that depend on a box appearing in the formatting structure
(like incrementing counters or running animations and transitions)
still operate on collapsed items.
<div class=example>
<p>In the following example,
a sidebar is sized to fit its content.
<a class=css data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visufx.html#propdef-visibility title=visibility>visibility: collapse</a> is used to dynamically hide parts of a navigation sidebar
without affecting its width, even though the widest item (“Architecture”)
is in a collapsed section.
</p><figure>
<figcaption>Sample rendering for example code below</figcaption>
<div id=visibility-collapse-example>
<nav>
<ul>
<li id=nav-about><a href=#nav-about>About</a>
<ul>
<li><a href=#>History</a>
<li><a href=#>Mission</a>
<li><a href=#>People</a>
</ul>
<li id=nav-projects><a href=#nav-projects>Projects</a>
<ul>
<li><a href=#>Art</a>
<li><a href=#>Architecture</a>
<li><a href=#>Music</a>
</ul>
<li id=nav-interact><a href=#nav-interact>Interact</a>
<ul>
<li><a href=#>Blog</a>
<li><a href=#>Forums</a>
<li><a href=#>Events</a>
</ul>
</ul>
</nav>
<article>
Interesting Stuff to Read
</article>
</div>
</figure>
<pre><style>
@media (min-width: 60em) {
/* <a href=http://www.w3.org/TR/css3-mediaqueries/#width>two column layout only when enough room</a> (relative to default text size) */
header + div { display: flex; }
#main {
flex: 1; /* <a href=#flexibility>Main takes up all remaining space</a> */
order: 1; /* <a href=#order-property>Place it after (to the right of) the navigation</a> */
min-width: 12em; /* Optimize main content area sizing */
}
}
/* menu items use flex layout so that visibility:collapse will work */
nav > ul > li {
display: flex;
flex-flow: column;
}
/* dynamically collapse submenus when not targetted */
nav > ul > li:not(:target):not(:hover) > ul {
visibility: collapse;
}
</style>
…
</header>
<div>
<article id="main">
Interesting Stuff to Read
</article>
<nav>
<ul>
<li id="nav-about"><a href="#nav-about">About</a>
…
<li id="nav-projects"><a href="#nav-projects">Projects</a>
<ul>
<li><a href="…">Art</a>
<li><a href="…">Architecture</a>
<li><a href="…">Music</a>
</ul>
<li id="nav-interact"><a href="#nav-interact">Interact</a>
…
</ul>
</nav>
</div>
<footer>
…
</pre>
</div>
<p>
To compute the size of the strut, flex layout is first performed with all items uncollapsed,
and then re-run with each collapsed item replaced by a strut that maintains
the original cross-size of the item’s original line.
See the <a href=#layout-algorithm>Flex Layout Algorithm</a>
for the normative definition of how <span class=css>visibility:collapse</span>
interacts with flex layout.
<p class=note>
Note that using <span class=css>visibility:collapse</span> on any flex items
will cause the flex layout algorithm to repeat partway through,
re-running the most expensive steps.
It’s recommended that authors continue to use <span class=css>display:none</span> to hide items
if the items will not be dynamically collapsed and uncollapsed,
as that is more efficient for the layout engine.
(Since only part of the steps need to be repeated when <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visufx.html#propdef-visibility title=visibility>visibility</a> is changed,
however, 'visibility: collapse' is still recommended for dynamic cases.)
<h3 class="heading settled" data-level=4.5 id=min-size-auto><span class=secno>4.5. </span><span class=content>
Implied Minimum Size of Flex Items</span><a class=self-link href=#min-size-auto></a></h3>
<p>To provide a more reasonable default minimum size for <a data-link-type=dfn href=#flex-item title="flex items">flex items</a>,
this specification introduces a new <a class=css data-link-for=min-width data-link-type=maybe href=#valdef-min-width-min-height-auto title=auto>auto</a> value
as the initial value of the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-min-width title=min-width>min-width</a> and <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-min-height title=min-height>min-height</a> properties defined in CSS 2.1. <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a></p>
<table class="definition propdef partial"><tr><th>Name:<td><a class=css data-link-type=property href=http://dev.w3.org/csswg/css2/visudet.html#propdef-min-width title=min-width>min-width</a>, <a class=css data-link-type=property href=http://dev.w3.org/csswg/css2/visudet.html#propdef-min-height title=min-height>min-height</a><tr><th>New values:<td class=prod>auto<tr><th>New initial value:<td>auto<tr><th>New computed value:<td>the percentage as specified or the absolute length or a keyword</table>
<dl data-dfn-for="min-width min-height" data-dfn-type=value>
<dt><dfn class=css data-dfn-for="min-width min-height" data-dfn-type=value data-export="" id=valdef-min-width-min-height-auto>auto<a class=self-link href=#valdef-min-width-min-height-auto></a></dfn>
<dd>
On a <a data-link-type=dfn href=#flex-item title="flex item">flex item</a> whose <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-overflow-3/#overflow0 title=overflow>overflow</a> is <span class=css data-link-for=overflow>visible</span> in the <a data-link-type=dfn href=#main-axis title="main axis">main axis</a>,
when specified on the <a data-link-type=dfn href=#flex-item title="flex item’s">flex item’s</a> main-axis min-size property,
the following table gives the minimum size:
<table class=data>
<colgroup span=2></colgroup>
<colgroup span=1></colgroup>
<thead>
<tr>
<th>Clamped Size
<th>Transferred Size
<th>Minimum Size
<tbody>
<tr>
<td>
<td>
<td><var>content size</var>
<tr>
<td>✓
<td>
<td>min(<var>clamped size</var>, <var>content size</var>)
<tr>
<td>
<td>✓
<td>min(<var>transferred size</var>, <var>content size</var>)
<tr>
<td>✓
<td>✓
<td>min(<var>clamped size</var>, <var>content size</var>)
</table>
<p>Where:</p>