CSS box shadow generator

Color and opacity are separate on purpose: the picker carries the hue, the opacity field multiplies the alpha, and the engine emits one rgba() per layer, so dialing a stack down does not mean re-picking twelve colors. The drop-shadow chain is an equivalent, not a match: drop-shadow() takes no spread and no inset, it follows the alpha shape of the element instead of drawing a rectangle, and chained drop-shadows compound, each drawing on the last. Where layers cannot convert, the output says exactly which and why instead of approximating.