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Summary
The flex
CSS property is a shorthand property specifying the ability of a flex item to alter its dimensions to fill available space. Flex items can be stretched to use available space proportional to their flex grow factor or their flex shrink factor to prevent overflow.
Initial value | as each of the properties of the shorthand:
|
---|---|
Applies to | flex items, including in-flow pseudo-elements |
Inherited | no |
Media | visual |
Computed value | as each of the properties of the shorthand:
|
Animation type | as each of the properties of the shorthand:
|
Canonical order | order of appearance in the formal grammar of the values |
See Using CSS flexible boxes for more properties and information.
Syntax
/* 0 0 auto */ flex: none; /* One value, unitless number: flex-grow */ flex: 2; /* One value, width/height: flex-basis */ flex: 10em; flex: 30px; flex: auto; flex: content; /* Two values: flex-grow | flex-basis */ flex: 1 30px; /* Two values: flex-grow | flex-shrink */ flex: 2 2; /* Three values: flex-grow | flex-shrink | flex-basis */ flex: 2 2 10%; /* Global values */ flex: inherit; flex: initial; flex: unset;
Values
<'flex-grow'>
- Defines the
flex-grow
of the flex item. See<number>
for more details. Negative values are considered invalid. Defaults to1
when omitted. <'flex-shrink'>
- Defines the
flex-shrink
of the flex item. See<number>
for more details. Negative values are considered invalid. Defaults to1
when omitted. <'flex-basis'>
- Defines the
flex-basis
of the flex item. Any value valid forwidth
andheight
properties are accepted. A preferred size of0
must have a unit to avoid being interpreted as a flexibility. Defaults to0%
when omitted. none
- This keyword computes to
0 0 auto
. -
Formal syntax
none | [ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]
Example
#flex-container { display: -webkit-flex; display: flex; -webkit-flex-direction: row; flex-direction: row; } #flex-container > .flex-item { -webkit-flex: auto; flex: auto; } #flex-container > .raw-item { width: 5rem; }
<div id="flex-container"> <div class="flex-item" id="flex">Flex box (click to toggle raw box)</div> <div class="raw-item" id="raw">Raw box</div> </div>
var flex = document.getElementById("flex"); var raw = document.getElementById("raw"); flex.addEventListener("click", function() { raw.style.display = raw.style.display == "none" ? "block" : "none"; });
#flex-container { width: 100%; font-family: Consolas, Arial, sans-serif; } #flex-container > div { border: 1px solid #f00; padding: 1rem; } #flex-container > .raw-item { border: 1px solid #000; }
Result
Specifications
Specification | Status | Comment |
---|---|---|
CSS Flexible Box Layout Module The definition of 'flex' in that specification. |
Candidate Recommendation | Initial definition |
Browser compatibility
Feature | Firefox (Gecko) | Chrome | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 18.0 (18.0)[1] 20.0 (20.0) 28.0 (28.0)[2] |
21.0-webkit 29.0 |
10.0-ms[3] 11.0[3] |
12.10 |
6.1-webkit |
Feature | Firefox Mobile (Gecko) | Android | IE Phone | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|
Basic support | ? | 4.4 | 11 | 12.10 | 7.1-webkit |
[1] In Gecko 18.0 (Firefox 18.0 / Thunderbird 18.0 / SeaMonkey 2.15) and 19.0 (Firefox 19.0 / Thunderbird 19.0 / SeaMonkey 2.16) flexbox support is hidden behind the about:config
preference layout.css.flexbox.enabled
, defaulting to false
.
[2] Multi-line flexbox is supported since Gecko 28.0 (Firefox 28.0 / Thunderbird 28.0 / SeaMonkey 2.25).
In addition to the unprefixed support, Gecko 48.0 (Firefox 48.0 / Thunderbird 48.0 / SeaMonkey 2.45) added support for a -webkit
prefixed version of the property for web compatibility reasons behind the preference layout.css.prefixes.webkit
, defaulting to false
. Since Gecko 49.0 (Firefox 49.0 / Thunderbird 49.0 / SeaMonkey 2.46) the preference defaults to true
.
[3] Internet Explorer 10-11 (but not 12+) ignores uses of calc()
in the flex-basis part of the flex
syntax. This can be worked around by using the longhand properties instead of the shorthand. See Flexbug #8 for more info. Furthermore a flex
declaration with a unitless value in its flex-basis
part is considered syntactically invalid in those versions and will thus be ignored. A workaround is to always include a unit in the flex-basis
part of the flex
shorthand value. See Flexbug #4 for more info.