width

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

* Some parts of this feature may have varying levels of support.

The width CSS property specifies the width of an element. By default, the property defines the width of the content area. If box-sizing is set to border-box, however, it instead determines the width of the border area.

css
/* <length> values */
width: 300px;
width: 25em;

/* <percentage> value */
width: 75%;

/* Keyword values */
width: 25em border-box;
width: 75% content-box;
width: max-content;
width: min-content;
width: available;
width: fit-content;
width: auto;

/* Global values */
width: inherit;
width: initial;
width: unset;

Examples

備註: min-widthmax-width 會覆寫 width.

預設值auto
Applies toall elements but non-replaced inline elements, table rows, and row groups
繼承與否no
Percentagesrefer to the width of the containing block
Computed valuea percentage or auto or the absolute length
Animation typea length, percentage or calc();

Syntax

The width property is specified as either:

Values

<length>

Defines the width as an absolute value.

<percentage>

Defines the width as a percentage of the containing block's width. If the width of the containing block depends on the width of the element, the resulting layout is undefined.

border-box 實驗性質

If present, the preceding <length> or <percentage> is applied to the element's border box.

content-box 實驗性質

If present, the preceding <length> or <percentage> is applied to the element's content box.

auto

The browser will calculate and select a width for the specified element.

fill 實驗性質

Use the fill-available inline size or fill-available block size, as appropriate to the writing mode.

max-content 實驗性質

The intrinsic preferred width.

min-content 實驗性質

The intrinsic minimum width.

available 實驗性質

The containing block width minus horizontal margin, border and padding.

fit-content 實驗性質

The larger of: the intrinsic minimum width

  • the smaller of the intrinsic preferred width and the available width

Formal syntax

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-name> || <anchor-size> ]? , <length-percentage>? )

<calc-size-basis> =
<intrinsic-size-keyword> |
<calc-size()> |
any |
<calc-sum>

<calc-sum> =
<calc-product> [ [ '+' | '-' ] <calc-product> ]*

<anchor-name> =
<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

範例

預設寬度

css
p.goldie {
  background: gold;
}
html
<p class="goldie">The Mozilla community produces a lot of great software.</p>

像素和相對大小

css
.px_length {
  width: 200px;
  background-color: red;
  color: white;
  border: 1px solid black;
}

.em_length {
  width: 20em;
  background-color: white;
  color: red;
  border: 1px solid black;
}
html
<div class="px_length">Width measured in px</div>
<div class="em_length">Width measured in em</div>

百分比

css
.percent {
  width: 20%;
  background-color: silver;
  border: 1px solid red;
}
html
<div class="percent">Width in percentage</div>

內容最大值

css
p.maxgreen {
  background: lightgreen;
  width: intrinsic; /* Safari/WebKit uses a non-standard name */
  width: -moz-max-content; /* Firefox/Gecko */
  width: -webkit-max-content; /* Chrome */
}
html
<p class="maxgreen">The Mozilla community produces a lot of great software.</p>

內容最小值

css
p.minblue {
  background: lightblue;
  width: -moz-min-content; /* Firefox */
  width: -webkit-min-content; /* Chrome */
}
html
<p class="minblue">The Mozilla community produces a lot of great software.</p>

規範

Specification
CSS Box Sizing Module Level 4
# width-height-keywords
CSS Box Sizing Module Level 4
# sizing-values

瀏覽器相容性

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
width
anchor-size()
Experimental
auto
fit-content
fit-content()
Experimental
Is animatable
max-content
min-content
stretch

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
No support
No support
Experimental. Expect behavior to change in the future.
See implementation notes.
User must explicitly enable this feature.
Uses a non-standard name.
Requires a vendor prefix or different name for use.
Has more compatibility info.

參考