CSS box-decoration-break

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The box-decoration-break property is one of the properties introduced in CSS3. It allows developers to specify what happens to an element when it is broken due to a page break or column break, or for inline elements, a line break.

More specifically, the box-decoration-break property allows developers to specify whether the box fragments are treated as broken fragments of one continuous box, or whether each fragment appears as its own box (i.e. each fragment maintains the border, padding, and other properties as though it's a stand alone box).

The box-decoration-break allows you to maintain various properties across any fragments.

Without the box-decoration-break property (or with its value set to slice), boxes are usually "sliced" whenever they encounter a break.

For example, imagine a <div> element within a multi-column layout. The element contains so much text, that it spans over many columns. And imagine that the div has padding and a border applied to it. When you view this div in a browser, you're disappointed to see that, when it breaks over to a new column, it is "sliced". The border and padding is removed on each fragment. In many cases, you might prefer these properties to be maintained across all fragments. This is where the box-decoration-break can come in handy. By using this property with a value of clone, you can maintain the borders, padding, drop shadows, border images, and border radius across page/column/line breaks.

Syntax

Possible Values

slice: This keyword specifies that the box will be "sliced" across it's many fragments (if any). In other words, the box fragments won't maintain the padding, border, box-shadow, border-radius, and border-image properties across each fragment. Also, any background or background-image is drawn once and each fragment shows a small piece of the background.
clone: The box-decoration-break (with a value of clone) allows you to maintain the padding, border, box-shadow, border-radius, and border-image properties within each fragment. It also allows any background to be drawn independently in each fragment of the element. A no-repeat background-image will be rendered once in each fragment of the element.

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: slice
Applies To: All elements
Inherited?: No
Media: Visual
Animatable: No

Example Code

Basic CSS

Working Example within an HTML Document

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This example uses vendor prefixes due to lack of browser support for the official standard at the time of writing.

CSS Specifications

The box-decoration-break property is defined in CSS Fragmentation Module Level 3 (W3C Candidate Recommendation, 14 January 2016)

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.