body {
  	background-image: url('/images/grey-pattern-bg-tiling.jpg');
    background-attachment: fixed;
}

.main-div {
	position: fixed; /* or absolute */
	top: 50%;
	left: 50%;
	/* bring your own prefixes */
	transform: translate(-50%, -50%);
}

.api {
  	background-image: url('/images/api-illustration.gif');
    background-repeat: no-repeat;
    background-attachment: fixed;
  	background-size: cover;
}