outline-width

The outline-width CSS property sets the width (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.

/* 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;

Syntax

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

Values

thin

Depends on the user agent. Typically 1px in desktop browsers like Firefox.

medium

Depends on the user agent. Typically 3px in desktop browsers like Firefox.

thick

Depends on the user agent. Typically 5px in desktop browsers like Firefox.

<length>

The width of the outline specified as a <length>.

Formal syntax

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

Examples

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="twoem">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;
}
#twoem {
  outline-width: 1.2em;
}

Specifications

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.