flex-basis
The flex-basis
CSS property sets the initial main size of a flex item. It sets the size of the content box unless otherwise set with box-sizing
.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
Note: in case both flex-basis
(other than auto
) and width
(or height
in case of flex-direction: column
) are set for an element, flex-basis
has priority.
Syntax
/* Specify <'width'> */
flex-basis: 10em;
flex-basis: 3px;
flex-basis: auto;
/* Intrinsic sizing keywords */
flex-basis: fill;
flex-basis: max-content;
flex-basis: min-content;
flex-basis: fit-content;
/* Automatically size based on the flex item’s content */
flex-basis: content;
/* Global values */
flex-basis: inherit;
flex-basis: initial;
flex-basis: unset;
The flex-basis
property is specified as either the keyword content
or a <'width'>
.
Values
<'width'>
- An absolute
<length>
, a<percentage>
of the parent flex container's main size property, or the keywordauto
. Negative values are invalid. Defaults toauto
. content
- Indicates automatic sizing, based on the flex item’s content.
-
Note: This value was not present in the initial release of Flexible Box Layout, and thus some older implementations will not support it. The equivalent effect can be had by using
auto
together with a main size (width or height) ofauto
.History:
- Originally,
flex-basis:auto
meant "look at mywidth
orheight
property". - Then,
flex-basis:auto
was changed to mean automatic sizing, and "main-size" was introduced as the "look at mywidth
orheight
property" keyword. It was implemented in bug 1032922. - Then, that change was reverted in bug 1093316, so
auto
once again means "look at mywidth
orheight
property"; and a newcontent
keyword is being introduced to trigger automatic sizing. (bug 1105111 covers adding that keyword).
- Originally,
Formal definition
Initial value | auto |
---|---|
Applies to | flex items, including in-flow pseudo-elements |
Inherited | no |
Percentages | refer to the flex container's inner main size |
Computed value | as specified, but with relative lengths converted into absolute lengths |
Animation type | a length, percentage or calc(); |
Formal syntax
content | <'width'>
Examples
Setting flex item initial sizes
HTML
<ul class="container">
<li class="flex flex1">1: flex-basis test</li>
<li class="flex flex2">2: flex-basis test</li>
<li class="flex flex3">3: flex-basis test</li>
<li class="flex flex4">4: flex-basis test</li>
<li class="flex flex5">5: flex-basis test</li>
</ul>
<ul class="container">
<li class="flex flex6">6: flex-basis test</li>
</ul>
CSS
.container {
font-family: arial, sans-serif;
margin: 0;
padding: 0;
list-style-type: none;
display: flex;
flex-wrap: wrap;
}
.flex {
background: #6AB6D8;
padding: 10px;
margin-bottom: 50px;
border: 3px solid #2E86BB;
color: white;
font-size: 14px;
text-align: center;
position: relative;
}
.flex:after {
position: absolute;
z-index: 1;
left: 0;
top: 100%;
margin-top: 10px;
width: 100%;
color: #333;
font-size: 12px;
}
.flex1 {
flex-basis: auto;
}
.flex1:after {
content: 'auto';
}
.flex2 {
flex-basis: max-content;
}
.flex2:after {
content: 'max-content';
}
.flex3 {
flex-basis: min-content;
}
.flex3:after {
content: 'min-content';
}
.flex4 {
flex-basis: fit-content;
}
.flex4:after {
content: 'fit-content';
}
.flex5 {
flex-basis: content;
}
.flex5:after {
content: 'content';
}
.flex6 {
flex-basis: fill;
}
.flex6:after {
content: 'fill';
}
Results
Specifications
Specification | Status | Comment |
---|---|---|
CSS Flexible Box Layout Module The definition of 'flex-basis' in that specification. |
Candidate Recommendation | Initial definition |
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
width