Fix icon and styling in browser notifications banner (#29658)

app/javascript/styles/mastodon/components.scss

@@ -8581,6 +8581,12 @@ noscript {
     color: $darker-text-color;
     margin-bottom: 15px;
     text-align: center;
+
+    .icon {
+      width: 20px;
+      height: 20px;
+      vertical-align: middle;
+    }
   }
 }