body {
  background-image: url('test.jpg');
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-position: center;
 background-size: cover;
}	

.centerimg {
  position: fixed;
  top: 50%;
  left: 50%;
  /* bring your own prefixes */
  transform: translate(-50%, -50%);
max-width: 25%;
height:auto;
}

.topcenter {
  position: fixed;
  top: 50%;
  left: 50%;
  /* bring your own prefixes */
  transform: translate(-50%, -50%);

width: 100px;
height: auto;

}