flex-basis
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2015.
CSS 属性 flex-basis
指定了 flex 元素在主轴方向上的初始大小。如果不使用 box-sizing
改变盒模型的话,那么这个属性就决定了 flex 元素的内容盒(content-box)的尺寸。
尝试一下
备注:当一个元素同时被设置了 flex-basis
(除值为 auto
外) 和 width
(或者在 flex-direction: column
情况下设置了height
) , flex-basis
具有更高的优先级。
语法
css
/* 指定<'width'> */
flex-basis: 10em;
flex-basis: 3px;
flex-basis: auto;
/* 固有的尺寸关键词 */
flex-basis: fill;
flex-basis: max-content;
flex-basis: min-content;
flex-basis: fit-content;
/* 在 flex item 内容上的自动尺寸 */
flex-basis: content;
/* 全局数值 */
flex-basis: inherit;
flex-basis: initial;
flex-basis: unset;
取值
<'width'>
-
width 值可以是
<length>
; 该值也可以是一个相对于其父弹性盒容器主轴尺寸的百分数
。负值是不被允许的。默认为auto
。 content
-
基于 flex 的元素的内容自动调整大小。
**备注:**由于最初规范中没有包括这个值,在一些早期的浏览器实现的 flex 布局中,content 值无效,可以利用设置 (width 或 height) 为 auto 达到同样的效果。
备注: 简史
- 最初,"flex-basis:auto" 的含义是 "参照我的
width
和height
属性". - 在此之后,"flex-basis:auto" 的含义变成了自动尺寸,而 "main-size" 变成了 "参照我的
width
和height
属性"。实际执行于 bug 1032922. - 然后呢,这个更改又在 bug 1093316 中被撤销了,所以 "auto" 变回了原来的含义; 而一个新的关键字 'content' 变成了自动尺寸。 (Firefox bug 1105111 包括了增加这个关键字).
- 最初,"flex-basis:auto" 的含义是 "参照我的
规范
flex-basis =
content |
<'width'>
<width> =
auto |
<length-percentage [0,∞]> |
min-content |
max-content |
fit-content( <length-percentage [0,∞]> ) |
<calc-size()> |
<anchor-size()>
<length-percentage> =
<length> |
<percentage>
<calc-size()> =
calc-size( <calc-size-basis> , <calc-sum> )
<anchor-size()> =
anchor-size( [ <anchor-element> || <anchor-size> ]? , <length-percentage>? )
<calc-size-basis> =
<intrinsic-size-keyword> |
<calc-size()> |
any |
<calc-sum>
<calc-sum> =
<calc-product> [ [ '+' | '-' ] <calc-product> ]*
<anchor-element> =
<dashed-ident>
<anchor-size> =
width |
height |
block |
inline |
self-block |
self-inline
<calc-product> =
<calc-value> [ [ '*' | '/' ] <calc-value> ]*
<calc-value> =
<number> |
<dimension> |
<percentage> |
<calc-keyword> |
( <calc-sum> )
<calc-keyword> =
e |
pi |
infinity |
-infinity |
NaN
示例
HTML
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
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: 20px;
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: 18px;
}
.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/-webkit-fill-available/-moz-available";
}
结果
规范
Specification |
---|
CSS Flexible Box Layout Module Level 1 # flex-basis-property |
浏览器兼容性
BCD tables only load in the browser
参见
- CSS 弹性盒子指南:Basic Concepts of Flexbox
- CSS 弹性盒子指南:Controlling Ratios of flex items along the main axis
width