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The flex
CSS shorthand property sets how a flex item will grow or shrink to fit the space available in its flex container.
Try it
Constituent properties
This property is a shorthand for the following CSS properties:
- flex-grow
- flex-shrink
- flex-basis
Syntax
css
/* Keyword values */flex: auto;flex: initial;flex: none;/* One value, unitless number: flex-growflex-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 valid value for <flex-grow>: then the shorthand expands to
flex: <flex-grow> 1 0
. - a valid value for <flex-basis>: then the shorthand expands to
flex: 1 1 <flex-basis>
. - the keyword
none
or one of the global keywords.
- a valid value for <flex-grow>: then the shorthand expands to
- Two-value syntax:
- The first value must be a valid value for flex-grow.
- The second value must be one of:
- a valid value for flex-shrink: then the shorthand expands to
flex: <flex-grow> <flex-shrink> 0
. - a valid value for flex-basis: then the shorthand expands to
flex: <flex-grow> 1 <flex-basis>
.
- a valid value for flex-shrink: then the shorthand expands to
- Three-value syntax: the values must be in the following order:
- a valid value for flex-grow.
- a valid value for flex-shrink.
- a valid value for flex-basis.
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 to
1
when omitted. (initial is0
) - <'flex-shrink'>
-
Defines the flex-shrink of the flex item. Negative values are considered invalid. Defaults to
1
when omitted. (initial is1
) - <'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 to0
when omitted. (initial isauto
)
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
flex =
none |
[ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]<flex-grow> =
<number [0,∞]><flex-shrink> =
<number [0,∞]><flex-basis> =
content |
<'width'><width> =
auto |
<length-percentage [0,∞]> |
min-content |
max-content |
fit-content( <length-percentage [0,∞]> )<length-percentage> =
<length> |
<percentage>
Examples
Setting flex: auto
This example shows how a flex item with flex: auto
grows to absorb any free space in the container.
HTML
html
<div id="flex-container"> <div id="flex-auto">flex: auto (click to toggle raw box)</div> <div id="flex-initial">flex: initial</div></div>
CSS
css
#flex-container { display: flex; font-family: Consolas, Arial, sans-serif;}#flex-container > div { padding: 1rem;}#flex-auto { flex: auto; border: 1px solid #f00;}#flex-initial { border: 1px solid #000;}
JavaScript
js
const flexAuto = document.getElementById("flex-auto");const flexInitial = document.getElementById("flex-initial");flexAuto.addEventListener("click", () => { flexInitial.style.display = flexInitial.style.display === "none" ? "block" : "none";});
Result
The flex container contains two flex items:
- "flex: auto" has a
flex
value of auto - "flex: initial" has a
flex
value of initial
The "flex: initial" item takes up as much space as its width requires, but does not expand to take up any more space. All the remaining space is taken up by "flex: auto".
When you click "flex: auto", we set "flex: initial"'s display property to none
, removing it from the layout. The "flex: auto" item then expands to occupy all the available space in the container.
Specifications
Specification |
---|
CSS Flexible Box Layout Module Level 1 # flex-property |
Browser compatibility
BCD tables only load in the browser
See also
- CSS Flexbox Guide: Basic Concepts of Flexbox
- CSS Flexbox Guide: Controlling Ratios of flex items along the main axis