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flex

The flex CSS shorthand property sets how a flex item will grow or shrink to fit the space available in its flex container.

Constituent properties

This property is a shorthand for the following CSS properties:

Syntax

/* Keyword values */
flex: auto;
flex: initial;
flex: none;

/* One value, unitless number: flex-grow */
flex: 2;

/* One value, width/height: flex-basis */
flex: 10em;
flex: 30%;
flex: min-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;

The flex property may be specified using one, two, or three values.

Values

initial
The item is sized according to its width and height properties. It shrinks to its minimum size to fit the container, but does not grow to absorb any extra free space in the flex container. This is equivalent to setting "flex: 0 1 auto".
auto
The item is sized according to its width and height properties, but grows to absorb any extra free space in the flex container, and shrinks to its minimum size to fit the container. This is equivalent to setting "flex: 1 1 auto".
none
The item is sized according to its width and height properties. It is fully inflexible: it neither shrinks nor grows in relation to the flex container. This is equivalent to setting "flex: 0 0 auto".
<'flex-grow'>
Defines the flex-grow of the flex item. Negative values are considered invalid. Defaults to 1 when omitted. (initial is 0)
<'flex-shrink'>
Defines the flex-shrink of the flex item. Negative values are considered invalid. Defaults to 1 when omitted. (initial is 1)
<'flex-basis'>
Defines the flex-basis of the flex item. A preferred size of 0 must have a unit to avoid being interpreted as a flexibility. Defaults to 0 when omitted. (initial is auto)

Description

For most purposes, authors should set flex to one of the following values: auto, initial, none, or a positive unitless number. To see the effect of these values, try resizing the flex containers below:

By default flex items don't shrink below their minimum content size. To change this, set the item's min-width or min-height.

Formal definition

Initial value as each of the properties of the shorthand:
Applies to flex items, including in-flow pseudo-elements
Inherited no
Computed value as each of the properties of the shorthand:
Animation type as each of the properties of the shorthand:

Formal syntax

none | [ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]

Examples

Setting flex: auto

HTML

<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>

CSS

#flex-container {
  display: flex;
  flex-direction: row;
}

#flex-container > .flex-item {
  flex: auto;
}

#flex-container > .raw-item {
  width: 5rem;
}

Result

Specifications

Specification Status Comment
CSS Flexible Box Layout Module
The definition of 'flex' in that specification.
Candidate Recommendation Initial definition

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
flex 29
29
21
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
12
12
12
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
20
20
Since Firefox 28, multi-line flexbox is supported.
Before Firefox 32, Firefox wasn't able to animate values starting or stopping at 0.
Until Firefox 61, flex items that are sized according to their content are sized using fit-content, not max-content.
18 — 28
Disabled
Disabled From version 18 until version 28 (exclusive): this feature is behind the layout.css.flexbox.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
49
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
48
Prefixed Disabled
Prefixed Implemented with the vendor prefix: -webkit-
Disabled From version 48: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.
11
11
Internet Explorer 11 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.
Internet Explorer 11 considers a unitless value in the flex-basis part to be syntactically invalid (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.
10
Prefixed
Prefixed Implemented with the vendor prefix: -ms-
Internet Explorer 10 and 11 ignore 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.
Internet Explorer 10 and 11 consider a unitless value in the flex-basis part to be syntactically invalid (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.
12.1 9
9
6.1
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
flex 4.4
4.4
≤37
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
29
29
25
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
20
20
Since Firefox 28, multi-line flexbox is supported.
Before Firefox 32, Firefox wasn't able to animate values starting or stopping at 0.
Until Firefox 61, flex items that are sized according to their content are sized using fit-content, not max-content.
18 — 28
Disabled
Disabled From version 18 until version 28 (exclusive): this feature is behind the layout.css.flexbox.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
49
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
48
Prefixed Disabled
Prefixed Implemented with the vendor prefix: -webkit-
Disabled From version 48: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.
12.1 9
9
7
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
2.0
2.0
1.5
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-

See also

© 2005–2020 Mozilla and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/CSS/flex