use property that will always be defined in my append header hack

frontend/viewer/src/lib/append-head-hack.ts

@@ -1,10 +1,11 @@
 if (import.meta.env.DEV) {
   //when in dev mode, svelte and vite want to put style sheets in the head
   //however blazor will remove them, so we need to put them in the body instead
+  // eslint-disable-next-line @typescript-eslint/unbound-method
   const headerAppend = document.head.appendChild;
   document.head.appendChild = function newAppend<T extends Node>(node: T) {
     //this is used for both svelte and vite imports
-    if (node.tagName === 'STYLE') {
+    if (node.nodeName === 'STYLE') {
       document.getElementById('svelte-app')?.appendChild(node);
     } else {
       headerAppend.call(document.head, node);