【CSS】脱jQueryでアイテムの全体画像とズーム画像をカーテンアニメーション後に並べて表示する方法のデモページ

.block {
  display: flex;
  max-width: 1200px;
  width: 100%;
  margin: 50px auto 0;
}

.text {
  width: 40%;
  margin: 100px 0 0;
  text-align: center;
  font-size: 20px;
}

.img {
  position: relative;
  display: flex;
  width: 60%;
}

.img:after {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  left: 0;
  bottom: 0;
  transition: all .7s cubic-bezier(.90,-.025,.45,1) .8s;
  background: #fff;
  background-attachment: fixed;
  z-index: 2;
}

.img-main {
  background: url("/demo01/demo-curtain-11/a.jpg") no-repeat center;
  background-size: cover;
}

.img-main {
  position: relative;
  width: 62%;
}

.img-sub {
  position: absolute;
  top: 0;
  right: 0;
  width: 100%;
  height: 100%;
  z-index: 1;
  transition: all .7s cubic-bezier(.80,-.05,.25,.99) 1.4s;
  background: url("/demo01/demo-curtain-11/b.jpg") no-repeat center right;
  background-size: cover;
}

.img-sub img,
.img-main img {
  opacity: 0;
}

.active .img:after {
  left: 100%;
}

.active .img-sub {
  width: 38%;
}

@media screen and (max-width:640px){
  .block {
    flex-wrap: wrap;
    max-width: 100%;
  }
  .text {
    width: 100%;
    margin: 30px 0 0;
    order: 2;
  }

  .img {
    width: 100%;
    order: 1;
  }
}

window.onload = function() {
  document.getElementById("block").classList.add("active")
};