スクロールで縮むヘッダー

<div class="d03-01-03-stage">
          <header class="d03-01-03-header">
            <span class="d03-01-03-logo">COMPANY</span>
            <nav class="d03-01-03-nav">
              <a href="#" onclick="return false">サービス</a>
              <a href="#" onclick="return false">実績</a>
              <a href="#" onclick="return false">お問い合わせ</a>
            </nav>
          </header>
          <div class="d03-01-03-scroll">
            <div class="d03-01-03-body">
              <p>↓ この領域をスクロール</p>
              <div class="d03-01-03-block"></div>
              <div class="d03-01-03-block"></div>
              <div class="d03-01-03-block"></div>
              <div class="d03-01-03-block"></div>
            </div>
          </div>
        </div>

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