Why use 2 box-shadow in paper

[Gaubee]

This Code:

    &.mui-z-depth-1 {
        .lh-box-shadow(0 1px 4px rgba(0, 0, 0, 0.24)); 
        & > .mui-z-depth-bottom { .lh-box-shadow(0 1px 6px rgba(0, 0, 0, 0.12)); }
    }

I can't understand why use two box-shadow. In Google material, It just like this:

button{
    box-shadow: 0 2px 5px 0 rgba(0, 0, 0, 0.26);
}

[hai-cea]

The upper and lower shadows were specified on the previous version of the material design specs. It doesn't seem to be there anymore, but I believe if you look at the photoshop files here: http://www.google.com/design/spec/resources/sticker-sheets-icons.html you will see 2 shadows.