Stack as many layers as you need, because one shadow is not how light works — real depth comes from a tight dark layer for contact and a wide faint one for the room around it.
Real shadows are several soft layers, not one hard one — a tight dark layer for contact and a wide faint one for the room.
The CSS
box-shadow: 0px 4px 12px 0px rgba(26, 26, 23, 0.1);
Set what you want and the result appears as you go. Nothing needs uploading because there is nothing to upload — you are describing what to make, not sending us anything.
Your browser does all the work locally, using your own operating system where randomness is involved. Nothing is requested from a server, so nobody else has a copy of what you made.
Take the result to your clipboard or save it as a file. Nothing is kept — refresh the page and it’s gone, so save what you need before you leave.