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outline-width

The CSS outline-width property sets the thickness of an element's outline. An outline is a line that is drawn around an element, outside the border.

Try it

It is often more convenient to use the shorthand property outline when defining the appearance of an outline.

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;
outline-width: initial;
outline-width: revert;
outline-width: revert-layer;
outline-width: unset;

The outline-width property is specified as any one of the values listed below.

Values

<length>: The width of the outline specified as a <length>.
thin: Depends on the user agent. Typically equivalent to 1px in desktop browsers (including Firefox).
medium: Depends on the user agent. Typically equivalent to 3px in desktop browsers (including Firefox).
thick: Depends on the user agent. Typically equivalent to 5px in desktop browsers (including Firefox).

Formal definition

Initial value	`medium`
Applies to	all elements
Inherited	no
Computed value	an absolute length; if the keyword `none` is specified, the computed value is `0`
Animation type	a length

Formal syntax

outline-width = 
  <line-width>  

<line-width> = 
  <length [0,∞]>  |
  thin            |
  medium          |
  thick

Examples

Setting an element's outline width

HTML

<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="em">1.2em</span>

CSS

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;
}

#em {
  outline-width: 1.2em;
}

Result

Specifications

Specification
CSS Basic User Interface Module Level 4 # outline-width

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`outline-width`	1	12	1.5 Before Firefox 88, an outline does not follow the shape of `border-radius`. 1-3.6	8	7	1.2	37	18	4 Before Firefox 88, an outline does not follow the shape of `border-radius`.	14	1	1.0