Property Reference - CSS Reference - page 224

Name
outline
Values:
<'outline-color'> || <'outline-style'> || <'outline-width'>
Initial value:
Not defined for shorthand properties
Applies to:
All elements
Inherited:
No
Computed value:
See individual properties
Description:
This is a shorthand property that defines the overall outline for an element. The most common
use of outlines is to indicate which form element or hyperlink currently has focus (accepts
keyboard input). Outlines can be of irregular shape, and no matter how thick, they do not
change or otherwise affect the placement of elements.
Examples:
*[href]:focus {outline: 2px dashed invert;}
form:focus {outline: outset cyan 0.25em;}