body {
  background:
  url(../gr_img/bg_footer_img.png) right bottom no-repeat,
  url(../gr_img/bg_footer.jpg) left bottom repeat-x,
  url(../gr_img/bg_is_cate.jpg) center top no-repeat,
  url(../gr_img/bg_gnavi.jpg) left 500px repeat-x,
  url(../gr_img/bg_html.jpg) left top repeat;
}

#main_img {
  position: absolute;
  z-index: 0;
  top: 0;
  left: 50%;
  margin-left: -683px;
  width: 1366px;
  height: 500px;
}