スクロールで出現するCTA付きヘッダー

<div class="d03-01-12-stage">
          <header class="d03-01-12-bar">
            <span class="d03-01-12-logo">STUDIO</span>
            <nav class="d03-01-12-nav">
              <a href="#" onclick="return false">サービス</a>
              <a href="#" onclick="return false">実績</a>
            </nav>
            <a href="#" class="d03-01-12-cta" onclick="return false">無料相談</a>
          </header>
          <div class="d03-01-12-scroll">
            <div class="d03-01-12-body">
              <p>↓ この領域をスクロール</p>
              <div class="d03-01-12-block"></div>
              <div class="d03-01-12-block"></div>
              <div class="d03-01-12-block"></div>
            </div>
          </div>
        </div>

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        .d03-01-12-bar{
          position:absolute;top:0;left:0;right:0;z-index:2;
          display:flex;align-items:center;gap:16px;
          height:56px;padding:0 16px;background:#fff;box-shadow:0 1px 4px rgba(0,0,0,.08);
        }
        .d03-01-12-logo{font-weight:800;letter-spacing:.1em;color:#111827;font-size:14px}
        .d03-01-12-nav{display:flex;gap:14px;margin-right:auto}
        .d03-01-12-nav a{color:#374151;text-decoration:none;font-size:12px;font-weight:600}
        .d03-01-12-cta{
          padding:8px 16px;border-radius:999px;background:#2563eb;color:#fff;
          font-size:12px;font-weight:700;text-decoration:none;white-space:nowrap;
          opacity:0;transform:translateX(16px);transition:opacity .35s ease,transform .35s ease;
        }
        .d03-01-12-stage.show-cta .d03-01-12-cta{opacity:1;transform:translateX(0)}
        .d03-01-12-scroll{position:absolute;inset:0;overflow-y:auto;padding-top:56px}
        .d03-01-12-body{padding:16px}
        .d03-01-12-body p{font-size:12px;color:#64748b;margin:0 0 12px;text-align:center}
        .d03-01-12-block{height:90px;border-radius:8px;margin-bottom:12px;background:linear-gradient(135deg,#e2e8f0,#cbd5e1)}

(function(){
        var stage=document.querySelector('.d03-01-12-stage');
        if(!stage)return;
        var scroller=stage.querySelector('.d03-01-12-scroll');
        scroller.addEventListener('scroll',function(){
          stage.classList.toggle('show-cta',scroller.scrollTop>30);
        });
      })();