fix: 公告栏横幅改为页面上方流式布局，不再遮挡导航

astro-template/src/components/Header.astro

@@ -4,17 +4,20 @@ import home from "../data/home.json";
 import design from "../data/design.json";
 const showAnnouncement = design.layout.announcementBar && home.announcement;
 ---
-{showAnnouncement && <div class="announcement-bar"><div class="container">{home.announcement}</div></div>}
-<header class="header">
-  <div class="container nav">
-    <a class="brand" href="#top"><span class="brand-mark">W</span><span>{company.name}</span></a>
-    <nav><a href="#about">关于我们</a><a href="#services">服务能力</a><a href="#advantages">企业优势</a><a href="articles/">文章</a></nav>
-    <a class="nav-action" href="#contact">联系合作 <span>↗</span></a>
-  </div>
-</header>
+<div class="masthead">
+  {showAnnouncement && <div class="announcement-bar"><div class="container">{home.announcement}</div></div>}
+  <header class="header">
+    <div class="container nav">
+      <a class="brand" href="#top"><span class="brand-mark">W</span><span>{company.name}</span></a>
+      <nav><a href="#about">关于我们</a><a href="#services">服务能力</a><a href="#advantages">企业优势</a><a href="articles/">文章</a></nav>
+      <a class="nav-action" href="#contact">联系合作 <span>↗</span></a>
+    </div>
+  </header>
+</div>
 <style>
+  .masthead { position: relative; z-index: 21; }
   .announcement-bar { position: relative; z-index: 21; padding: 9px 0; color: white; background: var(--color-primary-dark); font-size: 13px; font-weight: 600; text-align: center; letter-spacing: .02em; }
-  .header { position: absolute; z-index: 20; width: 100%; top: 0; }
+  .header { position: absolute; z-index: 20; width: 100%; top: 100%; }
   .nav { height: 88px; display: flex; align-items: center; justify-content: space-between; }
   .brand { display: flex; align-items: center; gap: 11px; font-size: 18px; font-weight: 800; letter-spacing: -.02em; }
   .brand-mark { display: grid; place-items: center; width: 34px; height: 34px; border-radius: 11px; color: white; background: var(--gradient-primary); box-shadow: 0 8px 22px rgba(112,40,255,.28); }