`outline-width` CSS property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It's been available across browsers since April 2017.

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.

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

Try it

outline-width: 12px;

outline-width: thin;

outline-width: medium;

outline-width: thick;

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box with an outline around it.
  </div>
</section>

#example-element {
  outline: 0.75em solid;
  padding: 0.75em;
  width: 80%;
  height: 100px;
}

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;

Values

This property is specified as one <line-width> value.

<line-width>: Defines the width of the outline, either as an explicit non-negative <length> or the keywords: thin, medium, or thick. The default is medium.

Formal definition

Initial value	medium
Applies to	all elements
Inherited	no
Computed value	the absolute `<length>`, snapped as a line width
Animation type	a <a href="/en-US/docs/Web/CSS/Reference/Values/length#interpolation" title="Values of the <length> CSS data type are interpolated as real, floating-point numbers.">length</a>

Formal syntax

outline-width = 
  <line-width>

<line-width> = 
  <length> |
  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	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on iOS	Samsung Internet	WebView Android	WebView on iOS
`outline-width`	1	12	1.5 Before Firefox 88, an outline does not follow the shape of `border-radius`. 1–3.6	7	1.2	18	4 Before Firefox for Android 88, an outline does not follow the shape of `border-radius`.	14	1	1.0	4.4	1
`medium`	1	12	1	15	1.2	18	4	14	1	1.0	4.4	1
`thick`	1	12	1	15	1.2	18	4	14	1	1.0	4.4	1
`thin`	1	12	1	15	1.2	18	4	14	1	1.0	4.4	1