Get the CSS and statuc stuff to work

webserver/static/error/error.js

@@ -0,0 +1,7 @@
+var error_close_buttons = document.getElementsByClassName("close_error_button");
+
+for (const close_button of error_close_buttons) {
+  close_button.addEventListener("click", function () {
+    this.parentElement.classList.add("hidden");
+  });
+}