/* Keyword value */
mask-border-repeat: stretch;
mask-border-repeat: repeat;
mask-border-repeat: round;
mask-border-repeat: space;

/* top and bottom | left and right */
mask-border-repeat: round stretch;

/* Global values */
mask-border-repeat: inherit;
mask-border-repeat: initial;
mask-border-repeat: revert;
mask-border-repeat: revert-layer;
mask-border-repeat: unset;

The mask-border-repeat property may be specified using one or two values chosen from the list of values below.

• When one value is specified, it applies the same behavior on all four sides.
• When two values are specified, the first applies to the top and bottom, the second to the left and right.

stretch

The source image's edge regions are stretched to fill the gap between each border.

repeat

The source image's edge regions are tiled (repeated) to fill the gap between each border. Tiles may be clipped to achieve the proper fit.

round

The source image's edge regions are tiled (repeated) to fill the gap between each border. Tiles may be stretched to achieve the proper fit.

space

The source image's edge regions are tiled (repeated) to fill the gap between each border. Extra space will be distributed in between tiles to achieve the proper fit.

mask-border-repeat = 
  [ stretch | repeat | round | space ]{1,2}  

This property doesn't appear to be supported anywhere yet. When it eventually starts to be supported, it will serve to define how the border mask slice will repeat around the border — i.e. will it just repeat, or be scaled slightly so a whole number of slices fits, or be stretched so one slice fits?

mask-border-repeat: round;

Chromium-based browsers support an outdated version of this property — mask-box-image-repeat — with a prefix:

-webkit-mask-box-image-repeat: round;

• mask-border
• mask-border-mode
• mask-border-outset
• mask-border-source
• mask-border-width