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: 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.
- One-value syntax: the value must be one of:
- a
<number>
: In this case it is interpreted asflex: <number> 1 0
; the<flex-shrink>
value is assumed to be 1 and the<flex-basis>
value is assumed to be0
. - one of the keywords:
none
,auto
, orinitial
.
- a
- 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>
.
- a
- Three-value syntax: the values must be in the following order:
- a
<number>
for<flex-grow>
. - a
<number>
for<flex-shrink>
. - a valid value for
width
for<flex-basis>
.
- a
Values
initial
- The item is sized according to its
width
andheight
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
andheight
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
andheight
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 to1
when omitted. <'flex-shrink'>
- Defines the
flex-shrink
of the flex item. Negative values are considered invalid. Defaults to1
when omitted. <'flex-basis'>
- Defines the
flex-basis
of the flex item. A preferred size of0
must have a unit to avoid being interpreted as a flexibility. Defaults to0
when omitted.
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:
<div class="flex-container"> <div class="item auto">auto</div> <div class="item auto">auto</div> <div class="item auto">auto</div> </div> <div class="flex-container"> <div class="item auto">auto</div> <div class="item initial">initial</div> <div class="item initial">initial</div> </div> <div class="flex-container"> <div class="item auto">auto</div> <div class="item auto">auto</div> <div class="item none">none</div> </div> <div class="flex-container"> <div class="item initial">initial</div> <div class="item none">none</div> <div class="item none">none</div> </div> <div class="flex-container"> <div class="item four">4</div> <div class="item two">2</div> <div class="item one">1</div> </div>
* { box-sizing: border-box; } .flex-container { background-color: #F4F7F8; resize: horizontal; overflow: hidden; display: flex; margin: 1em; } .item { margin: 1em; padding: 0.5em; width: 110px; min-width: 0; background-color: #1B5385; color: white; font-family: monospace; font-size: 13px; } .initial { flex: initial; } .auto { flex: auto; } .none { flex: none; } .four { flex: 4; } .two { flex: 2; } .one { flex: 1; }
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; }
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
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
flex | Chrome
Full support
29
| Edge
Full support
12
| Firefox
Full support
20
| IE
Full support
11
| Opera Full support 12.1 | Safari
Full support
9
| WebView Android
Full support
4.4
| Chrome Android
Full support
29
| Firefox Android
Full support
20
| Opera Android Full support 12.1 | Safari iOS
Full support
9
| Samsung Internet Android
Full support
2.0
|
Legend
- Full support
- Full support
- See implementation notes.
- See implementation notes.
- User must explicitly enable this feature.
- User must explicitly enable this feature.
- Requires a vendor prefix or different name for use.
- Requires a vendor prefix or different name for use.
See also
- CSS Flexbox Guide: Basic Concepts of Flexbox
- CSS Flexbox Guide: Controlling Ratios of flex items along the main axis