CSS border-image-slice

The border-image-slice 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-slice property is used for specifying inward offsets from the top, right, bottom, and left edges of the image, dividing it into nine regions: four corners, four edges and a middle.

The border-image-slice property is used in conjunction with the border-image-source, border-image-width, border-image-outset, 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

For all sides:

border-image-slice: value

Or to specify each side separately:

border-image-slice: top value right value bottom value left value

For more information, see the Possible Values section below.

Possible Values

Syntax:

The syntax for the possible values are:

border-image-slice: [<number> | <percentage>]{1,4} && fill?

So for example, to specify all sides at once:

border-image-slice: 30;

Or to specify each side separately:

border-image-slice: 20 30 40 25;

Values:

Here's an explanation of the allowed values:

<number>
Specifies pixels in the image (if the image is a raster image) or vector coordinates (if the image is a vector image).
<percentage>
A percentage value is relative to the size of the image: the width of the image for the horizontal offsets, the height for vertical offsets.
fill
This is an optional value that, if provided, specifies that the middle part of the border image should be preserved. If not specified, the middle part of the border image will be discarded (i.e. treated as empty).

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 inherit or initial, 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
100%
Applies To
All elements, except internal table elements when border-collapse is collapse
Inherited?
No
Media
Visual

Example Code

Basic CSS

border-image-slice: 28;

Working Example within an HTML Document

<!DOCTYPE html>
<title>Example</title>
<style>
.cool-border {
  width: 200px;
  padding: 30px;
  border: 1em double #edb742;
  border-image-source: url(/pix/css/css3/properties/border-image-1.png); 
  border-image-slice: 14; 
  border-image-width: 7px; 
  border-image-outset: 0; 
  border-image-repeat: round; 
}
</style>
<div class="cool-border">
  This box has a cool border?
</div>

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CSS Specifications

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.