body {
/* 画像ファイルの指定 */
  background-image: url(https://1gram.org/images/cmgson_bg.jpg);
  background-position: center center;
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: cover;
  background-color: #999999;
}

@media only screen and (max-width: 767px) {
  body {
    background-image: url(https://1gram.org/images/cmgson_bg.jpg);
  }
}


img {
  position: absolute;
  -webkit-backface-visibility: hidden;
  top: 100px;
  bottom: 0;
  left: 0;
  right: 0;
  margin: auto;
  max-width: 100%;
  max-height: 100%;
}

a:hover img.overwhite{
    cursor:pointer;
    filter: alpha(opacity=60);        /* ie lt 8 */
    -ms-filter: "alpha(opacity=60)";  /* ie 8 */
    -moz-opacity:0.6;                 /* FF lt 1.5, Netscape */
    -khtml-opacity: 0.6;              /* Safari 1.x */
    opacity:0.6;
    zoom:1;
}