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:

Initial value	medium
Applies to	all elements
Inherited	no
Media	visual, interactive
Computed value	an absolute length; if the keyword none is specified, the computed value is 0
Animation type	a length
Canonical order	the unique non-ambiguous order defined by the formal grammar

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

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;
}

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

Browser compatibility

[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.