#mainVisual {
  margin: 0 auto;
  width: 500px;
  height: 500px;
  position: relative;
}
#mainVisual div {
  position: absolute;
  filter: alpha(opacity=0);
  -moz-opacity: 0;
  opacity: 0;
}
#mainVisual :first-child {
  left: -4px;
}
#mainVisual :last-child {
  left: -4px;
}