outline

The outline CSS property is a shorthand property for setting one or more of the individual outline properties outline-style, outline-width, and outline-color in a single declaration.

/* width | style | color */
outline: 1px solid white;
/* Global values */
outline: inherit;
outline: initial;
outline: unset;

Outlines differ from borders in the following ways:

Outlines never take up space, as they are drawn outside of an element's content.
Outlines may be non-rectangular. They are rectangular in Gecko/Firefox, but Opera, for example, draws a non-rectangular shape around a construct like this:
TEXTTEXTTEXT

Initial value	as each of the properties of the shorthand: `outline-color`: `invert`, for browsers supporting it, `currentColor` for the other `outline-style`: `none` `outline-width`: `medium`
Applies to	all elements
Inherited	no
Media	visual, interactive
Computed value	as each of the properties of the shorthand: `outline-color`: For the keyword `invert`, the computed value is `invert`. For the color value, if the value is translucent, the computed value will be the `rgba()` corresponding one. If it isn't, it will be the `rgb()` corresponding one. The `transparent` keyword maps to `rgba(0,0,0,0)`. `outline-width`: an absolute length; if the keyword `none` is specified, the computed value is `0` `outline-style`: as specified
Animation type	as each of the properties of the shorthand: `outline-color`: a color `outline-width`: a length `outline-style`: discrete
Canonical order	order of appearance in the formal grammar of the values

Syntax

The outline property is specified as one, two, or three values from the list below. The order of the values does not matter.

Values

outline-width: Sets the thickness of the outline.
outline-style: Sets the style of the outline.
outline-color: Sets the color of the outline. Since Gecko 1.9 (Firefox 3), the value of the element's color property (foreground color) is used as the default.

Formal syntax

[ <'outline-color'> || <'outline-style'> || <'outline-width'> ]

Examples

outline: solid; | outline: dashed red; | outline: dotted 1px; | outline: ridge thick violet; | outline: custom 5px;

/* Two identical declarations */
:link:hover { outline: 1px solid #000; }
:link:hover { outline: solid black 1px; }

Specifications

Specification	Status	Comment
CSS Basic User Interface Module Level 3 The definition of 'outline' in that specification.	Candidate Recommendation	No change.
CSS Level 2 (Revision 1) The definition of 'outline' in that specification.	Recommendation	Initial definition.

Feature	Chrome	Edge	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	1.0	(Yes)	1.5 (1.8)^[1]	8.0	7.0	1.2 (125)

Feature	Android	Edge	Firefox Mobile (Gecko)	IE Phone	Opera Mobile	Safari Mobile
Basic support	1.0	(Yes)	1.0 (1.8) [1]	8.0	6.0	3.1

[1] In browsers previous to Gecko 1.8 (Firefox 1.5) a similar effect can be achieved using Mozilla CSS Extension -moz-outline.

Firefox includes absolutely positioned elements inside the outline (bug 687311).