セクション通過で配色が切り替わるヘッダー

<div class="d03-11-09-stage">
          <header class="d03-11-09-header">
            <span class="d03-11-09-logo">SECTION</span>
            <nav class="d03-11-09-nav">
              <a href="#" onclick="return false">はじめに</a>
              <a href="#" onclick="return false">夜景</a>
              <a href="#" onclick="return false">朝焼け</a>
            </nav>
          </header>
          <div class="d03-11-09-scroll">
            <div class="d03-11-09-sec d03-11-09-sec-a"><p>SECTION 1 / ライト</p></div>
            <div class="d03-11-09-sec d03-11-09-sec-b"><p>SECTION 2 / ダーク</p></div>
            <div class="d03-11-09-sec d03-11-09-sec-c"><p>SECTION 3 / サンセット</p></div>
          </div>
        </div>

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        .d03-11-09-stage.theme-warm .d03-11-09-nav a{color:#c2410c}
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        .d03-11-09-sec p{margin:0;font-size:12px;font-weight:700;color:#fff;letter-spacing:.06em}
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        .d03-11-09-sec-a p{color:#1e3a8a}
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        .d03-11-09-sec-c{background:linear-gradient(135deg,#fb923c,#f97316)}

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