CSS - outline-width

The outline-width CSS property is used to set the width of the outline of an element. An outline is a line that is drawn around elements, outside the border edge, to make the element stand out:

Examples

HTML Content

<span id="thin">thin</span>
<span id="medium">medium</span>
<span id="thick">thick</span>
<span id="twopixels">2px</span>
<span id="oneex">1ex</span>
<span id="twoem">2em</span>

CSS Content

span {
  outline-style: solid;
  display: inline-block;
  margin: 20px;
}

#thin {
  outline-width: thin;
}

#medium {
  outline-width: medium;
}

#thick {
  outline-width: thick;
}

#twopixels {
  outline-width: 2px;
}

#oneex {
  outline-width: 1ex;
}

#twoem {
  outline-width: 2em;
}

Syntax  

/* Keyword values */
outline-width: thin;
outline-width: medium;
outline-width: thick;

/* <length> values */
outline-width: 1px;
outline-width: 0.1em;

/* Global values */
outline-width: inherit;

Values

thin
Depends on the UA. Typically 1px in desktop browsers like Firefox.
medium
Depends on the UA. Typically 3px in desktop browsers like Firefox.
thick
Depends on the UA. Typically 5px in desktop browsers like Firefox.
<length>
See <length> values.

Formal syntax

<br-width>

where
<br-width> = <length> | thin | medium | thick

Description  

The outline-width CSS property is used to set the width of the outline of an element. An outline is a line that is drawn around elements, outside the border edge, to make the element stand out:

Initial valuemedium
Applies toall elements
Inheritedno
Mediavisual, interactive
Computed valuean absolute length; if the keyword none is specified, the computed value is 0
Animatableyes, as a length
Canonical orderthe unique non-ambiguous order defined by the formal grammar

Browser Compatibility  

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 1.0 1.5 (1.8)[1] 8.0 7.0 1.2 (125)
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? ? ? ? ?

[1] In browsers previous to Gecko 1.8 (Firefox 1.5) essentially the same effect can be achieved using Mozilla CSS Extension -moz-outline-width.

Specifications  

Specification Status Comment
CSS Basic User Interface Module Level 3
The definition of 'outline-width' in that specification.
Candidate Recommendation No change
CSS Transitions
The definition of 'outline-width' in that specification.
Working Draft Defines outline-width as animatable.
CSS Level 2 (Revision 1)
The definition of 'outline-width' in that specification.
Recommendation Initial definition

License

© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/css/outline-width