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                <div id="target" class="m-target">target</div>


                .m-target {
  /* ↓↓↓↓↓ フェードイン関連スタイル ↓↓↓↓↓ */
  opacity: 0;
  transform: translateY(20vh);
  visibility: hidden;
  transition: opacity 1200ms ease-out, transform 600ms ease-out, visibility 1200ms ease-out;
  will-change: opacity, transform, visibility;

  /* ↓↓↓↓↓ 装飾関連スタイル ↓↓↓↓↓ */
  display: flex;
  justify-content: center;
  align-items: center;
  width: 300px;
  height: 50px;
  margin: 100vh auto 80px;
  border-radius: 10px;
  background-color: #e17055;
  color: #fff;
  font-weight: bold;
  font-size: 32px;

  /* ↓↓↓↓↓ 表示領域に侵入したとき付与するクラス ↓↓↓↓↓ */
  &.is-visible {
    opacity: 1;
    transform: none;
    visibility: visible;



                function handleObserver (entries) {
  entries.forEach(entry => {
    if (entry.isIntersecting) {'is-visible');
    } else {'is-visible');

const observer = new IntersectionObserver(handleObserver);