左右にスライドする方向インジケータ

<div class="d08-13-03-stage">
          <div class="d08-13-03-scroll">
            <div class="d08-13-03-body">
              <p>↓↑ スクロールしてインジケータの動きを確認</p>
              <div class="d08-13-03-block"></div>
              <div class="d08-13-03-block"></div>
              <div class="d08-13-03-block"></div>
              <div class="d08-13-03-block"></div>
            </div>
          </div>
          <div class="d08-13-03-track"><span class="d08-13-03-knob">↑</span></div>
        </div>

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        .d08-13-03-body{padding:16px}
        .d08-13-03-body p{font-size:11.5px;color:#15803d;margin:0 0 12px;text-align:center}
        .d08-13-03-block{height:70px;border-radius:8px;margin-bottom:12px;background:linear-gradient(135deg,#dcfce7,#86efac)}
        .d08-13-03-track{
          position:absolute;left:50%;bottom:14px;transform:translateX(-50%);z-index:3;
          width:140px;height:34px;border-radius:17px;background:#dcfce7;
          display:flex;align-items:center;padding:0 2px;box-shadow:inset 0 1px 3px rgba(0,0,0,.08);
        }
        .d08-13-03-knob{
          width:30px;height:30px;border-radius:50%;flex:none;
          background:linear-gradient(135deg,#16a34a,#22c55e);color:#fff;font-size:13px;font-weight:700;
          display:flex;align-items:center;justify-content:center;
          transition:transform .3s cubic-bezier(.4,0,.2,1);
        }
        .d08-13-03-stage.is-down .d08-13-03-knob{transform:translateX(106px)}

(function(){
        var stage=document.querySelector('.d08-13-03-stage');
        if(!stage)return;
        var scroller=stage.querySelector('.d08-13-03-scroll');
        var knob=stage.querySelector('.d08-13-03-knob');
        var last=0;
        scroller.addEventListener('scroll',function(){
          var top=scroller.scrollTop;
          if(top>last+2){stage.classList.add('is-down');knob.textContent='↓';}
          else if(top<last-2){stage.classList.remove('is-down');knob.textContent='↑';}
          last=top<=0?0:top;
        });
      })();