flex

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 the concatenation of the initial values of its longhand properties:
    • flex-grow: 0
    • flex-shrink: 1
    • flex-basis: auto
  • Applies to flex items, including in-flow pseudo-elements
  • Inherited no
  • Media visual
  • Computed value as each of the properties of the shorthand:
    • flex-grow: as specified
    • flex-shrink: as specified
    • flex-basis: as specified, with lengths made absolute
  • Animatable as each of the properties of the shorthand:
    • flex-grow: yes, as a number, except between 0 and other values
    • flex-shrink: yes, as a number, except between 0 and other values
    • flex-basis: yes, as a length, percentage or calc(); when both values are lengths, they are interpolated as lengths; when both values are percentages, they are interpolated as percentages; otherwise, both values are converted into a calc() function that is the sum of a length and a percentage (each possibly zero), and these calc() functions have each half interpolated as real numbers.
  • Canonical order order of appearance in the formal grammar of the values

See Using CSS flexible boxes for more properties and information.

Syntax

Formal syntax: none | [ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]
flex: none                                            /* value 'none' case */
flex: <'flex-grow'>                                   /* One value syntax, variation 1 */
flex: <'flex-basis'>                                  /* One value syntax, variation 2 */
flex: <'flex-grow'> <'flex-basis'>                    /* Two values syntax, variation 1 */
flex: <'flex-grow'> <'flex-shrink'>                   /* Two values syntax, variation 2 */
flex: <'flex-grow'> <'flex-shrink'> <'flex-basis'>    /* Three values syntax */

flex: inherit

Values

<'flex-grow'>
See <number> for more details. Negative values are considered invalid.
<'flex-shrink'>
See <number> for more details. Negative values are considered invalid. This value is optional.
<'flex-basis'>
Defines the flex basis of the flex item. Any value valid for width and height properties are accepted. A preferred size of 0 must have a unit to avoid being interpreted as a flexibility. Defaults to 0%.
none
This keyword computes to 0 0 auto.
auto
This keyword is equivalent to 1 1 auto.
initial
This keyword is equivalent to 0 1 auto.
Note: The default value of <'flex-basis'> in the 'flex' shorthand is different from the initial value of the flex-basis property.
Note: The <'flex-grow'> and <'flex-shrink'> properties are set to '1' if omitted.

Examples

<style type="text/css">
  #flex-container {
    width:100%;

    /* flexbox specific properties */
    display: -webkit-flex;
    display: flex;
    -webkit-flex-direction: row;
    flex-direction: row;
  }
  #flex-container .flex-item {
    border:1px solid #f00;

    /* flexbox specific properties */
    -webkit-flex: auto;
    flex: auto;
  }
</style>

<div id="flex-container">
  <div class="flex-item">Flex Box 1</div>
  <div class="flex-item">Flex Box 2</div>
</div>

FIXME: : Improve on these examples.

Specifications

Specification Status Comment
CSS Flexible Box Layout Module Candidate Recommendation  

Browser compatibility

Feature Firefox (Gecko) Chrome Internet Explorer Opera Safari
Basic support 18.0 (18.0) (behind a pref) [1, 2]
20.0 (20.0) [2]
21.0-webkit
29.0
10.0-ms
11.0
12.10 6.1-webkit
Feature Firefox Mobile (Gecko) Android IE Phone Opera Mobile Safari Mobile
Basic support ? ? Not supported 12.10 Not supported

[1] To activate flexbox support for Firefox 18 and 19, the user has to change the about:config preference "layout.css.flexbox.enabled" to true.

[2] Multi-line flexbox are supported since Firefox 28.

See also

Document Tags and Contributors

Last updated by: andRyanMiller,
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