mask-mode

The mask-mode CSS property is set on the element being masked. It sets whether the mask reference defined by the mask-image is treated as a luminance or alpha mask.

A mask transfers its transparency, and depending on the mask type, its luminance, to the element it is masking. If the mask is of type image, by default the alpha values of the mask image determine the visibility of each part of the masked element: where the mask is opaque, the corresponding part of the masked element is visible; where the mask is translucent, the element is as well, with those areas of the element being hidden. This is the default behavior for <image> masks when the mask-mode property is set to or defaults to match-source, and it is always the case when the mask-mode is explicitly set to alpha.

Syntax example: mask-mode: alpha;