CSS page indent shadow at top/bottom for scrolling section

gistfile1.css

/* top and bottom */
background: 
  linear-gradient(hsla(0,0%,100%,0) 15px, white 40px),
  linear-gradient(to top, hsla(0,0%,100%,0) 15px, white 40px) bottom;
  radial-gradient(at 50% 0, rgba(0,0,0,.2), transparent 70%),
  radial-gradient(at 50% 100%, rgba(0,0,0,.2), transparent 70%) bottom;
background-repeat: no-repeat;
background-size: 100% 50%, 100% 50%, 100% 14px, 100% 14px;
background-attachment: local, local, scroll, scroll;

/* top */
background:
  linear-gradient(white, white),
  radial-gradient(at 50% 0, rgba(0,0,0,.2), transparent 70%);
background-size: 100% 50px, 100% 15px;
background-repeat: no-repeat;
background-attachment: local, scroll;