nav.js: hide pre#code-pre via CSS immediately

Author: pepc84

assets/nav.js

@@ -62,6 +62,7 @@
     style.textContent = `
       html.dark-pre body { background:#1a1a2e !important; }
       pre#code-pre { display:none !important; }
+      pre#code-pre { display:none !important; }
       #site-nav {
         border-bottom: 1px solid #e0e0e0;
         padding: 0 2rem;