@charset "utf-8";
img.bg {
  /* Set rules to fill background */
  /*min-height: 100%;*/
  /*min-width: 320px;*/
  /* Set up proportionate scaling */
  width:auto;
  height:110%;
  /* Set up positioning */
  position: fixed;
  /* またはabsolute; */
  top: 0;
  left:0;
  padding:0 50%;
  margin-left:-20%;
  background-color:#FFFFFF;
  z-index:1000;  
}

@media screen and (max-width:999px){
  img.bg {
  	height:auto;
  	width:100%;
	margin:0;
	padding:0 0 100% 0;
	background-color:#000;
	}
}