下で隠れ上で現れるヘッダー

<div class="d03-11-01-stage">
          <header class="d03-11-01-header">
            <span class="d03-11-01-logo">SHOWCASE</span>
            <nav class="d03-11-01-nav">
              <a href="#" onclick="return false">サービス</a>
              <a href="#" onclick="return false">実績</a>
              <a href="#" onclick="return false">お問合せ</a>
            </nav>
          </header>
          <div class="d03-11-01-scroll">
            <div class="d03-11-01-body">
              <p>↓ 下にスクロールすると隠れ、↑ 上にスクロールすると現れます</p>
              <div class="d03-11-01-block"></div>
              <div class="d03-11-01-block"></div>
              <div class="d03-11-01-block"></div>
              <div class="d03-11-01-block"></div>
              <div class="d03-11-01-block"></div>
            </div>
          </div>
        </div>

.prev.d03-11-01{padding:0;display:block}
        .d03-11-01-stage{position:relative;width:100%;height:100%;min-height:260px;overflow:hidden;background:#f8fafc}
        .d03-11-01-header{
          position:absolute;top:0;left:0;right:0;z-index:2;
          display:flex;align-items:center;justify-content:space-between;
          height:54px;padding:0 18px;background:#fff;
          box-shadow:0 2px 8px rgba(0,0,0,.08);
          transform:translateY(0);
          transition:transform .3s ease;
        }
        .d03-11-01-stage.hide-header .d03-11-01-header{transform:translateY(-100%)}
        .d03-11-01-logo{font-weight:800;letter-spacing:.1em;color:#0f172a;font-size:14px}
        .d03-11-01-nav{display:flex;gap:14px}
        .d03-11-01-nav a{color:#334155;text-decoration:none;font-size:11.5px;font-weight:600}
        .d03-11-01-nav a:hover{color:#2563eb}
        .d03-11-01-scroll{position:absolute;inset:0;overflow-y:auto;padding-top:54px}
        .d03-11-01-body{padding:16px}
        .d03-11-01-body p{font-size:11.5px;color:#64748b;margin:0 0 12px;text-align:center}
        .d03-11-01-block{
          height:70px;border-radius:8px;margin-bottom:12px;
          background:linear-gradient(135deg,#dbeafe,#93c5fd);
        }

(function(){
        var stage=document.querySelector('.d03-11-01-stage');
        if(!stage)return;
        var scroller=stage.querySelector('.d03-11-01-scroll');
        var last=0;
        scroller.addEventListener('scroll',function(){
          var top=scroller.scrollTop;
          if(top>last&&top>40){
            stage.classList.add('hide-header');
          }else{
            stage.classList.remove('hide-header');
          }
          last=top<=0?0:top;
        });
      })();