flex
The flex
CSS shorthand property sets how a {{glossary("flex item")}} will grow or shrink to fit the space available in its flex container.
{{EmbedInteractiveExample("pages/css/flex.html")}}
Constituent properties
This property is a shorthand for the following CSS properties:
- {{cssxref("flex-grow")}}
- {{cssxref("flex-shrink")}}
- {{cssxref("flex-basis")}}
Syntax
/* Keyword value */
flex: none; /* 0 0 auto */
/* One value, unitless number: flex-grow
flex-basis is then equal to 0%. */
flex: 2; /* 2 1 0% */
/* One value, width/height: flex-basis */
flex: auto; /* 1 1 auto */
flex: 10em; /* 1 1 10em */
flex: 30%;
flex: min-content;
/* Two values: flex-grow | flex-basis */
flex: 1 30px; /* 1 1 30px */
/* Two values: flex-grow | flex-shrink */
flex: 2 2; /* 2 2 0% */
/* Three values: flex-grow | flex-shrink | flex-basis */
flex: 2 2 10%;
/* Global values */
flex: inherit;
flex: initial; /* 0 1 auto */
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 {{cssxref("<flex-grow>")}}: then, in all the browsers, the shorthand expands to
flex: <flex-grow> 1 0%
. However the specification says it should expand toflex: <flex-grow> 1 0
. - a valid value for {{cssxref("<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 {{cssxref("<flex-grow>")}}: then, in all the browsers, the shorthand expands to
-
Two-value syntax:
-
The first value must be a valid value for {{cssxref("flex-grow")}}.
-
The second value must be one of:
- a valid value for {{cssxref("flex-shrink")}}: then, in all the browsers, the shorthand expands to
flex: <flex-grow> <flex-shrink> 0%
. - a valid value for {{cssxref("flex-basis")}}: then the shorthand expands to
flex: <flex-grow> 1 <flex-basis>
.
- a valid value for {{cssxref("flex-shrink")}}: then, in all the browsers, the shorthand expands to
-
-
Three-value syntax: the values must be in the following order:
- a valid value for {{cssxref("flex-grow")}}.
- a valid value for {{cssxref("flex-shrink")}}.
- a valid value for {{cssxref("flex-basis")}}.
Values
<'flex-grow'>
- : Defines the {{cssxref("flex-grow")}} of the flex item. Negative values are considered invalid. Defaults to
1
when omitted. (initial is0
)
- : Defines the {{cssxref("flex-grow")}} of the flex item. Negative values are considered invalid. Defaults to
<'flex-shrink'>
- : Defines the {{cssxref("flex-shrink")}} of the flex item. Negative values are considered invalid. Defaults to
1
when omitted. (initial is1
)
- : Defines the {{cssxref("flex-shrink")}} of the flex item. Negative values are considered invalid. Defaults to
<'flex-basis'>
- : Defines the {{cssxref("flex-basis")}} of the flex item. Defaults to
0%
when omitted. The initial value isauto
.
- : Defines the {{cssxref("flex-basis")}} of the flex item. Defaults to
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 settingflex: 0 0 auto
.
- : The item is sized according to its
Commonly desired flexbox effects can be achieved using the following flex
values:
-
initial
: Flex item doesn't grow but can shrink. This default value expands toflex: 0 1 auto
. The item is sized according to itswidth
orheight
properties, depending on theflex-direction
. If there is negative available space, the item will shrink to its minimum size to fit within the container but will not grow to absorb any positive space available in the flex container. -
auto
: Flex item can grow and shrink. This value expands toflex: 1 1 auto
. The item is sized according to itswidth
orheight
properties, depending on theflex-direction
, but grows to absorb available positive space in the flex container or shrink down to its minimum size to fit the container in the case of negative space. The flex item is fully flexible. -
none
: The flex item neither grows nor shrinks. This value expands toflex: 0 0 auto
. The item is sized according to itswidth
orheight
properties, depending on the direction of the flex container. The flex item is fully inflexible. -
flex: <number [1,∞]>
: The flex item's main size will be proportional to the number set. This value expands toflex: <number> 1 0
. This sets theflex-basis
to zero and makes the flex item flexible. The item will be at least as wide or tall as its minimum size, with the container's positive available space being proportionally distributed based on the growth factors of this item and its sibling flex items. If all the flex items use this pattern, all will be sized in proportion to their numeric values.[!WARNING] The browsers use
flex-basis
value0%
when theflex-basis
is not specified in aflex
value. This is not the same asflex-basis
value0
which is what the specification says. This may affect flex layout in some cases. See this effect demonstrated in the Flex-basis0
versus0%
example.
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;
}
{{EmbedLiveSample("Description", 1200, 400)}}
By default flex items don't shrink below their {{cssxref("min-content")}} size. To change this, set the item's {{cssxref("min-width")}} or {{cssxref("min-height")}}.
Formal definition
Formal syntax
Examples
Setting flex: auto
This example shows how a flex item with flex: auto
grows to absorb any free space in the container.
HTML
<div id="flex-container">
<div id="flex-auto">
flex: auto (click to remove/add the `flex: initial` box)
</div>
<div id="default">flex: initial</div>
</div>
CSS
body * {
padding: 1rem;
text-select: none;
box-sizing: border-box;
font-family: Consolas, Arial, sans-serif;
}
#flex-container {
border: 2px dashed gray;
display: flex;
}
#flex-auto {
cursor: pointer;
background-color: wheat;
flex: auto;
}
#default {
background-color: lightblue;
}
JavaScript
const flexAutoItem = document.getElementById("flex-auto");
const defaultItem = document.getElementById("default");
flexAutoItem.addEventListener("click", () => {
defaultItem.style.display =
defaultItem.style.display === "none" ? "block" : "none";
});
Result
The flex container contains two flex items:
- The
#flex-auto
item has aflex
value ofauto
. Theauto
value expands to1 1 auto
, i.e. the item is allowed to expand. - The
#default
item has noflex
value set so it defaults to theinitial
value. Theinitial
value expands to0 1 auto
, i.e. the item is not allowed to expand.
The #default
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 the #flex-auto
item.
When you click the #flex-auto
item, we set the #default
item's {{cssxref("display")}} property to none
, removing it from the layout. The #flex-auto
item then expands to occupy all the available space in the container. Clicking the #flex-auto
item again adds the #default
item back to the container.
{{EmbedLiveSample('Setting_flex_auto','100%','150')}}