The mask-border-source property is used to specify an image that is to be used as a mask border image. 2n572o

The mask border image is set to an element using the same steps used to set a border-image-repeat properties.

The mask-border-source property is usually set as part of the shorthand mask-border shorthand property’s entry.

An image that is an empty image (zero width or zero height), that fails to , is non-existent, or that cannot be displayed (e.g. because it is not in a ed image format) is ignored. It still counts as an mask border image but does not mask the element.

The application of the mask-border-source property to an element formatted with the CSS box model establishes a opacity property does, and all the element’s descendants are rendered together as a group with the masking applied to the group as a whole.

The mask-border-source property has no effect on the geometry or hit-testing of any element’s CSS boxes. Which means that it does not affect how the element responds to pointer events.

mask-border-source and the mask-image is applied to the element before or after mask-border-source. Both operation orders result in the same rendering.

Note that the mask-border-repeat.

mask-border-image: url(border-mask.png);
mask-border-image: none;
mask-border-image: linear-gradient(black, transparent); /* a linear gradient is an <image> */