CSS border-image-outset
The border-image-outset property is one of the properties introduced in CSS3 for the purposes of enabling images to be used on CSS borders.
The CSS border-image-outset property is used for defining how much a border image area extends beyond the border box.
The border-image-outset property is used in conjunction with the border-image-source, border-image-slice, border-image-width, and border-image-repeat properties in order to determine how the image will appear on the border.
Note that setting an image border will override any border that has been specified using the border-style properties. However, if the image cannot be loaded, or if the border-image-source value is none, the border styles will be used instead.
To save time (and use less code), use the border-image property to set all your background image properties at once.
Syntax
The formal grammar for this property is:
Below are some examples of usage.
One-Value Syntax
To set all four sides at once:
Example:
Two-Value Syntax
To specify the horizontal and vertical values separately:
Example:
Three-Value Syntax
To specify the top, vertical, and bottom values separately:
Example:
Four-Value Syntax
To specify all four sides separately:
Example:
Inherit Syntax
To inherit the values:
Possible Values
<number>- A number value represents a multiple of the
border-width. - <length>
- A length value specifies a fixed amount. For example,
1em
If this property has four values, they set the outsets on the top, right, bottom and left sides respectively. If the left is missing, it is the same as the right; if the bottom is missing, it is the same as the top; if the right is missing, it is the same as the top. For more information, see the Syntax section above.
In addition, all CSS properties also accept the following CSS-wide keyword values as the sole component of their property value:
initial- Represents the value specified as the property's initial value.
inherit- Represents the computed value of the property on the element's parent.
unset- This value acts as either
inheritorinitial, depending on whether the property is inherited or not. In other words, it sets all properties to their parent value if they are inheritable or to their initial value if not inheritable.
Basic Property Information
- Initial Value
0- Applies To
- All elements, except internal table elements when
border-collapseiscollapse - Inherited?
- No
- Media
- Visual
Example Code
Basic CSS
Working Example within an HTML Document
CSS Specifications
- The
border-image-outsetproperty is defined in CSS Backgrounds and Borders Module Level 3 (W3C Candidate Recommendation 9 September 2014)
Browser Support
The following table provided by Caniuse.com shows the level of browser support for this feature.
Vendor Prefixes
For maximum browser compatibility many web developers add browser-specific properties by using extensions such as -webkit- for Safari, Google Chrome, and Opera (newer versions), -ms- for Internet Explorer, -moz- for Firefox, -o- for older versions of Opera etc. As with any CSS property, if a browser doesn't support a proprietary extension, it will simply ignore it.
This practice is not recommended by the W3C, however in many cases, the only way you can test a property is to include the CSS extension that is compatible with your browser.
The major browser manufacturers generally strive to adhere to the W3C specifications, and when they support a non-prefixed property, they typically remove the prefixed version. Also, W3C advises vendors to remove their prefixes for properties that reach Candidate Recommendation status.
Many developers use Autoprefixer, which is a postprocessor for CSS. Autoprefixer automatically adds vendor prefixes to your CSS so that you don't need to. It also removes old, unnecessary prefixes from your CSS.
You can also use Autoprefixer with preprocessors such as Less and Sass.