mask-border-slice CSS property.

Values: [<number> | <percentage>]{1,4} fill?
Initial value: 0
Applies to: All elements. In SVG, it applies to container elements excluding the <defs> element and all graphics elements
Inherit: no
Percentages: refer to size of the mask border image
Animatable: no
Media: visual
Computed value: as specified

CSS Standards

CSS 1
CSS 2
CSS 2.1
CSS 3
Yes