width

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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.

/* <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;

注意: 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
Mediavisual
Computed valuea percentage or auto or the absolute length
Animation typea length, percentage or calc();
Canonical orderthe length or percentage before the keyword, if both are present

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
If present, the preceding <length> or <percentage> is applied to the element's border box.
content-box
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
Use the fill-available inline size or fill-available block size, as appropriate to the writing mode.
max-content
The intrinsic preferred width.
min-content
The intrinsic minimum width.
available
The containing block width minus horizontal margin, border and padding.
fit-content
The larger of:
  • the intrinsic minimum width
  • the smaller of the intrinsic preferred width and the available width

Formal syntax

[ <length> | <percentage> ] && [ border-box | content-box ]? | available | min-content | max-content | fit-content | auto

範例

預設寬度

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

像素和相對大小

.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;
}
<div class="px_length">Width measured in px</div>
<div class="em_length">Width measured in em</div>

百分比

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

內容最大值

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

內容最小值

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

規範

Specification Status Comment
CSS Basic Box Model
The definition of 'width' in that specification.
Working Draft Added the max-content, min-content, available, fit-content, border-box, content-box keywords.
CSS Transitions
The definition of 'width' in that specification.
Working Draft Lists width as animatable.
CSS Level 2 (Revision 1)
The definition of 'width' in that specification.
Recommendation Precises on which element it applies to.
CSS Level 1
The definition of 'width' in that specification.
Recommendation Initial definition.
CSS Intrinsic & Extrinsic Sizing Module Level 3
The definition of 'width' in that specification.
Working Draft Adds new sizing keywords for width and height.

瀏覽器相容性

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
widthChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 3.5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0
Animatable
Experimental
Chrome Full support 26Edge Full support 12Firefox Full support 16IE Full support 11Opera Full support 15Safari Full support 6.1WebView Android Full support 4.4Chrome Android Full support 26Firefox Android Full support 16Opera Android Full support 14Safari iOS Full support 6.1Samsung Internet Android Full support Yes
border-box
Experimental
Chrome No support NoEdge No support NoFirefox No support NoIE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoFirefox Android No support NoOpera Android ? Safari iOS No support NoSamsung Internet Android No support No
content-box
Experimental
Chrome No support NoEdge No support NoFirefox No support NoIE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoFirefox Android No support NoOpera Android ? Safari iOS No support NoSamsung Internet Android No support No
fill
ExperimentalNon-standard
Chrome Full support 46Edge No support NoFirefox No support NoIE No support NoOpera Full support 33Safari Full support 12WebView Android Full support 46Chrome Android Full support 46Firefox Android No support NoOpera Android ? Safari iOS Full support 12Samsung Internet Android Full support 5.0
fit-contentChrome Full support 46
Full support 46
Full support 22
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Edge No support NoFirefox Full support 3
Prefixed
Full support 3
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
IE No support NoOpera Full support 33
Full support 33
Full support 15
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Safari Full support 11
Full support 11
Full support 6.1
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
WebView Android Full support 46Chrome Android Full support 46Firefox Android Full support 4
Prefixed
Full support 4
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
Opera Android ? Safari iOS Full support 11
Full support 11
Full support 7
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Samsung Internet Android Full support 5.0
Alternate Name
Full support 5.0
Alternate Name
Alternate Name Uses the non-standard name: -webkit-fill-available
max-contentChrome Full support 46
Full support 46
Full support 22
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Edge No support NoFirefox Full support 66
Full support 66
Full support 3
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
IE No support NoOpera Full support 44Safari Full support 11
Full support 11
Full support 2
Alternate Name
Alternate Name Uses the non-standard name: intrinsic
WebView Android Full support 46Chrome Android Full support 46Firefox Android Full support 66
Full support 66
Full support 4
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
Opera Android Full support 43Safari iOS Full support 11
Full support 11
Full support 1
Alternate Name
Alternate Name Uses the non-standard name: intrinsic
Samsung Internet Android Full support 5.0
min-contentChrome Full support 46
Full support 46
Full support 22
Alternate Name
Alternate Name Uses the non-standard name: min-intrinsic
Edge No support NoFirefox Full support 66
Full support 66
Full support 3
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
IE No support NoOpera Full support 44Safari Full support 11
Full support 11
Full support 2
Alternate Name
Alternate Name Uses the non-standard name: min-intrinsic
WebView Android Full support 46Chrome Android Full support 46Firefox Android Full support 66
Full support 66
Full support 4
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
Opera Android Full support 43Safari iOS Full support 11
Full support 11
Full support 1
Alternate Name
Alternate Name Uses the non-standard name: min-intrinsic
Samsung Internet Android Full support 5.0
stretch
Experimental
Chrome Full support 22
Alternate Name
Full support 22
Alternate Name
Alternate Name Uses the non-standard name: -webkit-fill-available
Edge No support NoFirefox Full support 3
Alternate Name
Full support 3
Alternate Name
Alternate Name Uses the non-standard name: -moz-available
IE No support NoOpera Full support 15
Alternate Name
Full support 15
Alternate Name
Alternate Name Uses the non-standard name: -webkit-fill-available
Safari Full support 6.1
Prefixed
Full support 6.1
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
WebView Android Full support 4.4
Alternate Name
Full support 4.4
Alternate Name
Alternate Name Uses the non-standard name: -webkit-fill-available
Chrome Android Full support 25
Alternate Name
Full support 25
Alternate Name
Alternate Name Uses the non-standard name: -webkit-fill-available
Firefox Android Full support 4
Alternate Name
Full support 4
Alternate Name
Alternate Name Uses the non-standard name: -moz-available
Opera Android ? Safari iOS Full support 6.1
Prefixed
Full support 6.1
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Samsung Internet Android Full support 5.0

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.
Uses a non-standard name.
Uses a non-standard name.
Requires a vendor prefix or different name for use.
Requires a vendor prefix or different name for use.

參考