The border-image-outset CSS property sets the distance by which an element's border image is set out from its border box.
|Applies to||all elements, except internal table elements when border-collapse is collapse. It also applies to ::first-letter.|
The size of the border-image outset as a dimension — a number with a unit.
The size of the border-image outset as a multiple of the element's corresponding border-widths. For example, if an element has border-width: 1em 2px 0 1.5rem, and border-image-outset: 2, the final border-image-outset would be calculated as 2em 4px 0 3rem.