outline - CSS: Cascading Style Sheets 编辑

The outline CSS shorthand property set all the outline properties in a single declaration.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Constituent properties

This property is a shorthand for the following CSS properties:

• outline-color
• outline-style
• outline-width

Syntax

/* style */
outline: solid;

/* color | style */
outline: #f66 dashed;

/* style | width */
outline: inset thick;

/* color | style | width */
outline: green solid 3px;

/* Global values */
outline: inherit;
outline: initial;
outline: unset;

The outline property may be specified using one, two, or three of the values listed below. The order of the values does not matter.

Note: The outline will be invisible for many elements if its style is not defined. This is because the style defaults to none. A notable exception is input elements, which are given default styling by browsers.

Values

<'outline-color'>

Sets the color of the outline. Defaults to currentcolor if absent. See outline-color.

<'outline-style'>

Sets the style of the outline. Defaults to none if absent. See outline-style.

<'outline-width'>

Sets the thickness of the outline. Defaults to medium if absent. See outline-width.

Description

Borders and outlines are very similar. However, outlines differ from borders in the following ways:

• Outlines never take up space, as they are drawn outside of an element's content.
• According to the spec, outlines don't have to be rectangular, although they usually are.

As with all shorthand properties, any omitted sub-values will be set to their initial value.

Accessibility concerns

Assigning outline a value of 0 or none will remove the browser's default focus style. If an element can be interacted with it must have a visible focus indicator. Provide obvious focus styling if the default focus style is removed.

• How to Design Useful and Usable Focus Indicators

• WCAG 2.1: Understanding Success Criterion 2.4.7: Focus Visible

Formal definition

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
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

Formal syntax

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

Examples

Using outline to set a focus style

HTML

<a href="#">This link has a special focus style.</a>

CSS

a {
  border: 1px solid;
  border-radius: 3px;
  display: inline-block;
  margin: 10px;
  padding: 5px;
}

a:focus {
  outline: 4px dotted #e73;
  outline-offset: 4px;
  background: #ffa;
}

Result

Specifications

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

Browser compatibility

BCD tables only load in the browser

See also

• outline-color
• outline-style
• outline-width