flex property - CSS Reference

Definition and Usage

The flex CSS property specifies ability of a flex item to alter their dimensions to fill the 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 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

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>