Why does box-shadow take two comma separated values?

On the fCC applied visual design section, one of the lessons was on using box-shadows in CSS. I noticed that the line for box-shadow was

box-shadow: 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23);

Why does this take two comma separated set of values?

Hi @danielpyon
the comma is used to specify multiple box-shadow effects for the element(s) your selecting, for example, you want a div to have two box shadow’s one blue color and other red

div {
     box-shadow: 0 0 2px blue, 0 0 4px red;

you can play around with it to understand it

Oh, I get it… Thanks!