About Box-shadow first and second length

Question

you are described box-shadow first and second leng. your sentence is first length horizontal and second length vertical. but I were try your sample code and change first and second length then I saw first length vertical change second length horizantal change. so your description is false, I think. what is the true?

Answer 1

A box shadow can have 2,3,or 4 length values. If you give 2 they will be for the x and y values.
If 3 is given it is interpreted as a blur radius and if a fourth value is given it is interpreted as a spread radius. So if you had something like the following:
box-shadow: 50px 15px red;
Then you have the <offset-x> (horizontal) set to 50px, the <offset-y> (vertical) set to 15px and the color red.
Negative values can also be used.