why multipple layer box shadow code example

Example: multilayer shadow in css

/* Default box-shadow */
.box {
  box-shadow: 0 3px 3px rgba(0,0,0,0.2);
}

/* Create smoother box-shadows by layering multiple
 * shadows with gradually increasing radius and offset */
.shadow-5 {
  box-shadow: 0 1px 1px rgba(0,0,0,0.12), 
              0 2px 2px rgba(0,0,0,0.12), 
              0 4px 4px rgba(0,0,0,0.12), 
              0 8px 8px rgba(0,0,0,0.12),
              0 16px 16px rgba(0,0,0,0.12);
}