outline-width

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

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

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;
}

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	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android
`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	37