preload css

index.html

@@ -9,7 +9,7 @@
     <meta http-equiv="Content-Security-Policy"
         content="default-src 'none'; script-src 'self'; style-src 'self'; manifest-src 'self'; img-src 'self'" />
     <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=yes" />
-    <link rel="stylesheet" type="text/css" href="index.css" fetchpriority="high" referrerpolicy="no-referrer" />
+    <link rel="preload" type="text/css" href="index.css" fetchpriority="high" referrerpolicy="no-referrer" />
     <link rel="icon" href="icons/icon.svg" fetchpriority="low" referrerpolicy="no-referrer" />
     <link rel="manifest" href="app.webmanifest" type="application/manifest+json" fetchpriority="low"
         referrerpolicy="no-referrer" />