CSS Shadow Generator builds a layered box-shadow or text-shadow with a live preview. Adjust the offset, blur, spread, colour, and inset for each layer, stack as many as you like, and copy the declaration.
It runs in the page and remembers your last shadow. Nothing is uploaded.
text-shadow does not support them, so those controls only appear in box-shadow mode.
It reads box-shadow values with unitless or px lengths. Other units are treated as 0.
Pixels.
No. It is all local to your browser.