方向検知フェード式フローティングボタン

<div class="d08-13-02-stage">
          <div class="d08-13-02-scroll">
            <div class="d08-13-02-body">
              <p>↓ 下スクロールでボタンが消え / ↑ 上スクロールで再表示</p>
              <div class="d08-13-02-block"></div>
              <div class="d08-13-02-block"></div>
              <div class="d08-13-02-block"></div>
              <div class="d08-13-02-block"></div>
            </div>
          </div>
          <button type="button" class="d08-13-02-fab">資料請求</button>
        </div>

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        .d08-13-02-fab{
          position:absolute;right:16px;bottom:16px;z-index:3;
          background:linear-gradient(135deg,#c026d3,#7c3aed);color:#fff;border:none;
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          opacity:1;transform:translateY(0);transition:opacity .3s ease,transform .3s ease;
        }
        .d08-13-02-stage.is-down .d08-13-02-fab{opacity:0;transform:translateY(14px);pointer-events:none}

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