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                <div class="viewport">
  <p>詳しくはこちらの<a href="" target="_blank">ブログ記事</a>をご覧ください。</p>
  <div class="frame">
    <img src="" alt="" class="tanuki">



                html,body {
  margin: 0;
  height: 100%;

.viewport {
  height: 100%;
  overflow: auto;

.frame {
  height: 1000px;
  position: relative;

.tanuki {
  width: 100px;
  height: 100px;
  position: absolute;
  left: 0;
  top: 50%;
  transform: translate(-100%, -50%);
  transition: .3s;
  &.appear {
    transform: translate(-30%, -50%);


                const targets = document.querySelectorAll(".tanuki");
// IntersectionObserverに対応しているブラウザのみ、処理を実行
if ("IntersectionObserver" in window) {
	const options = {
		root: document.querySelector(".viewport"),
		rootMargin: "-50% 0%",
		threshold: 0.0
	const targetObserver = new IntersectionObserver(function(entries, observer) {
		entries.forEach(function(entry) {
			// この要素が画面に入ってきた場合
			if (entry.isIntersecting) {"appear");
			} else {"appear");
	}, options);
	targets.forEach(function(target) {
} else {
	targets.forEach(function(target) {