It's an purpose of spec, that creates multiple shadows in an element that extends the current purpose of box-shadow
The purpose is create an shadow, that fit with the left or the right side of the screen. Actually box-shadow just allow us to duplicate the element, not adjust the size of it's shadow
.element {
--shadow-size: <width> <height>;
}An shadow that starts from right to left, with `--shadow-size: 50vh auto; will get the half part of screen for this shadow.