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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.

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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-basis is then equal to 0. */
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: revert;
flex: revert-layer;
flex: unset;

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

  • One-value syntax: the value must be one of:
    • a <number>: In this case it is interpreted as flex: <number> 1 0; the flex-shrink value is assumed to be 1 and the flex-basis value is assumed to be 0.
    • a <width>: In this case it is interpreted as flex: 1 1 <width>; the flex-grow value is assumed to be 1 and the flex-shrink value is assumed to be 1.
    • one of the keywords: none, auto, or initial.
  • Two-value syntax:
    • The first value must be:
      • a <number> and it is interpreted as <flex-grow>.
    • The second value must be one of:
      • a <number>: then it is interpreted as <flex-shrink>.
      • a valid value for width: then it is interpreted as <flex-basis>.
  • Three-value syntax: the values must be in the following order:
    1. a <number> for <flex-grow>.
    2. a <number> for <flex-shrink>.
    3. a valid value for width for <flex-basis>.

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

flex = 
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

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
flex
29
21
12
12
49
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."]
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
["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
7
≤37
4.4
29
25
49
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."]
12.1
9
7
2.0
1.5

See also

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/CSS/flex